Light-emitting element, light-emitting device, electronic device and lighting device

Abstract

Light-emitting element comprising: a light-emitting layer between an anode and a cathode, wherein the light-emitting layer contains a first organic compound, a second organic compound and a light-emitting substance which converts triplet excitation energy into light emission, wherein the first organic compound and the second organic compound are mixed in the light-emitting layer, wherein a combination of the first organic compound and the second organic compound forms an exciplex, wherein the first organic compound comprises a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, wherein the six-membered nitrogen-containing heteroaromatic ring is pyrazine, pyridazine, triazine or tetrazine, wherein the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound, and wherein a difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.4 eV.

Description

Background of the invention 1. Field of the invention

[0001] The present invention relates to a light-emitting element, a light-emitting device, an electronic device and a lighting device. 2. Description of the state of the art

[0002] A light-emitting element containing an organic compound as a luminous body, with features such as thinness, lightness, fast response time, and low-voltage DC operation, is expected to be applied to a next-generation flat panel display. In particular, a display device in which light-emitting elements are arranged in a matrix is ​​expected to have advantages over a conventional liquid crystal display device, namely a wide viewing angle and excellent visibility.

[0003] The light-emitting mechanism of a light-emitting element is said to be as follows: When a voltage is applied between a pair of electrodes with an EL layer containing a luminous element provided therebetween, electrons injected from a cathode and holes injected from an anode recombine in the light-emitting center of the EL layer to form molecular excitons. When the molecular excitons return to the ground state, energy is released and light is emitted. The singlet excited state and the triplet excited state are known as excited states, and it is considered that light emission can be obtained from either of the excited states.

[0004] In order to improve element properties of such a light-emitting element, improvement of an element structure, development of a material, and the like have been actively carried out (see, for example, Patent Document 1 and Non-Patent Document 1). [Reference] [Patent document 1] JP 2010 - 182 699 A [Non-patent document 1] Chih-Hao Chang et al., Journal of Materials Chemistry 2012, Vol. 22, pp. 3832-3838. Summary of the invention

[0005] When developing light-emitting elements, one of the important points for commercialization is to improve the reliability of the elements. To improve the reliability of the elements, an element structure that can control the carrier balance in an EL layer of a light-emitting element and improve the recombination probability of the carriers is required. Therefore, it is a task to provide a highly reliable light-emitting element in the following way: An EL layer is formed to have a desired structure so that carriers are efficiently transferred in a light-emitting layer. High current efficiency (or high quantum efficiency) is also important to reduce the amount of current required to drive the element and improve reliability.

[0006] In one embodiment of the present invention, a light-emitting element with improved reliability is provided. Further, a light-emitting element with high current efficiency (or high quantum efficiency) is provided. Furthermore, an organic compound advantageously used in a light-emitting element which is an embodiment of the present invention is provided. In another embodiment of the present invention, a light-emitting element, a light-emitting device, an electronic device, or a lighting device with high emission efficiency and high reliability, which uses the above organic compound as an EL material, is provided. In another embodiment of the present invention, a novel light-emitting element and a novel light-emitting device are provided.It should be noted that the descriptions of these objects do not preclude the existence of further objects. In one embodiment of the present invention, it is unnecessary to fulfill all of the objects. Further objects are apparent from and can be derived from the explanations of the description, the drawings, the claims, and the like.

[0007] One embodiment of the present invention is a light-emitting element including a light-emitting layer between an anode and a cathode, wherein the light-emitting layer contains a first organic compound, a second organic compound, and a light-emitting substance that converts triplet excitation energy into light emission, wherein the first organic compound and the second organic compound are mixed in the light-emitting layer, wherein a combination of the first organic compound and the second organic compound forms an exciplex, wherein the first organic compound comprises a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, wherein the six-membered nitrogen-containing heteroaromatic ring is pyrazine, pyridazine, triazine, or tetrazine,wherein the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound. A difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.4 eV or less than or equal to 0.3 eV.

[0008] Another embodiment of the present invention is a light-emitting element comprising: a light-emitting layer between an anode and a cathode, wherein the light-emitting layer contains a first organic compound, a second organic compound, and a light-emitting substance that converts triplet excitation energy into light emission, wherein a combination of the first organic compound and the second organic compound forms an exciplex, wherein the first organic compound comprises a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, wherein the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound, and wherein a benzene ring is condensed with the six-membered nitrogen-containing heteroaromatic ring.A difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.4 eV or less than or equal to 0.3 eV.

[0009] In a preferred embodiment, the first organic compound has a six-membered nitrogen-containing heteroaromatic ring and a bicarbazole skeleton and does not have a triarylamine skeleton; and the second organic compound has a triarylamine skeleton.

[0010] In the above structure, the bicarbazole skeleton is preferably a 3,3'-bicarbazole skeleton or a 2,3'-bicarbazole skeleton.

[0011] In each of the above structures, the light-emitting substance is preferably a phosphorescent compound.

[0012] In each of the above structures, the EL layer preferably includes a hole-transport layer; the hole-transport layer is in contact with the light-emitting layer and contains a third organic compound having a hole-transport property; and the HOMO level of the third organic compound is lower than the HOMO level of the second organic compound.

[0013] In each of the above structures, the first organic compound is preferably represented by the following general formula (G0).

[0014] In the formula, A represents a dibenzo[f,h]quinoxalinyl group; R 1 to R 15independently represent hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group.

[0015] Preferably, the first organic compound is represented by the following general formula (G1).

[0016] In the formula, R 1 to R 24independently represents hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group.

[0017] Preferably, the first organic compound is represented by the following general formula (G2).

[0018] In the formula, R 1 to R 24independently represents hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group.

[0019] Preferably, the first organic compound is represented by the following general formula (G3).

[0020] In the formula, R 1 to R 24independently represents hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group.

[0021] Examples of the alkyl group having 1 to 6 carbon atoms in each of the above general formula (G0), general formula (G2), and general formula (G3) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a hexyl group. Examples of the cycloalkyl group having 5 to 7 carbon atoms include a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. Examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a tolyl group, a xylyl group, a biphenyl group, an indenyl group, a naphthyl group, and a fluorenyl group. Examples of the arylene group having 6 to 25 carbon atoms in Ar include 1,2-, 1,3- and 1,4-phenylene groups, 2,6-, 3,5- and 2,4-toluene groups, a 4,6-dimethylbenzene-1,3-diyl group, a 2,4,6-trimethylbenzene-1,3-diyl group, a 2,3,5,6-tetramethylbenzene-1,4-diyl group, 3,3'-, 3,4'- and 4,4'-biphenylene groups, a 1,1':3',1''-terbenzene-3,3''-diyl group, a 1,1':4',1''-terbenzene-3,3''-diyl group, a 1,1':4',1''-terbenzene-4,4''-diyl group, a 1,1':3',1'':3'',1'''-quaterbenzene-3,3'''-diyl group, a 1,1':3',1'':4'',1'''-quaterbenzene-3,4'''-diyl group, a 1,1':4',1'':4'',1'''-quaterbenzene-4,4'''-diyl group, 1,4-, 1,5-, 2,6- and 2,7-naphthylene groups, a 2,7-fluorenylene group, a 9,9-dimethyl-2,7-fluorenylene group, a 9,9-diphenyl-2,7-fluorenylene group, a 9,9-dimethyl-1,4-fluorenylene group, a spiro-9,9'-bifluorene-2,7-diyl group, a 9,10-dihydro-2,7-phenanthrenylene group, a 2,7-phenanthrenylene group, a 3,6-phenanthrenylene group, a 9,10-phenanthrenylene group, a 2,7-triphenylenylene group, a 3,6-triphenylenylene group, a 2,8-benzo[a]phenanthrenylene group, a 2,9-benzo[a]phenanthrenylene group and a 5,8-Benzo[c]phenanthrenylene group.,

[0022] The alkyl group having 1 to 6 carbon atoms, the cycloalkyl group having 5 to 7 carbon atoms, the aryl group having 6 to 13 carbon atoms, and the arylene group having 6 to 25 carbon atoms may each have a substituent. Examples of the substituent preferably include alkyl groups each having 1 to 6 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a hexyl group; cycloalkyl groups each having 5 to 7 carbon atoms, such as a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group; and aryl groups each having 6 to 13 carbon atoms forming a ring, such asa phenyl group, a tolyl group, a xylyl group, a biphenyl group, an indenyl group, a naphthyl group, a fluorenyl group and a 9,9-dimethylfluorenyl group.

[0023] Another embodiment of the present invention is a light-emitting device including the light-emitting element having any of the above structures and preferably a housing.

[0024] In addition to a light-emitting device including a light-emitting element, an embodiment of the present invention includes in its category an electronic device including the light-emitting device and a connection terminal or an operation button, and a lighting device including the light-emitting device and a housing. A light-emitting device in this specification refers to an image display device or a light source (e.g., a lighting device). In addition, a light-emitting device in its category includes all of the following modules: a module in which a light-emitting device is connected to a connector such as a connector;a flexible printed circuit (FPC) or a tape carrier package (TCP), a module in which a printed circuit board is provided at the end of a TCP, and a module in which an integrated circuit (IC) is directly mounted on a light-emitting element by a chip-on-glass (COG) process.

[0025] According to another embodiment of the present invention, a novel light-emitting element and a novel light-emitting device can be provided. It should be noted that the descriptions of these effects do not preclude the existence of other effects. An embodiment of the present invention may not necessarily achieve all of the above-mentioned effects. Other effects are apparent from and can be derived from the explanations of the specification, the drawings, the claims, and the like. Short description of the drawings Fig. 1 schematically shows a light-emitting layer of a light-emitting element. Fig. 2 schematically shows a light-emitting layer of a light-emitting element. Fig. 3A and Fig. 3B each represent the structure of a light-emitting element. Fig. 4A and Fig. 4B each represent the structure of a light-emitting element. Fig. 5 represents a light emitting device. Fig. 6A and Fig. 6B illustrate a light-emitting device. Fig. 7A, Fig. 7B, Fig. 7C, Fig. 7D, Fig. 7D' Fig. 1 and Fig. 7D' Fig. 2 each represent an electronic device. Fig. 8A to Fig. 8C represent an electronic device. Fig. 9 represents lighting devices. Fig. 10A and Fig. 10B are 1 H-NMR diagrams of a dibenzo[f,h]quinoxaline derivative represented by the structural formula (100). Fig. Figure 11 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (100). Fig. Figure 12 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (100). Fig. 13A and Fig. 13B are 1 H-NMR diagrams of a dibenzo[f,h]quinoxaline derivative represented by the structural formula (101). Fig. Figure 14 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (101). Fig. Figure 15 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (101). Fig. 16A and Fig. 16B are 1 H-NMR diagrams of a dibenzo[f,h]quinoxaline derivative represented by the structural formula (102). Fig. Figure 17 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (102). Fig. Figure 18 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (102). Fig. 19A and Fig. 19B are 1 H-NMR diagrams of a dibenzo[f,h]quinoxaline derivative represented by the structural formula (103). Fig. Figure 20 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (103). Fig. Figure 21 shows the UV-VIS absorption spectrum and emission spectrum of the dibenzo[f,h]quinoxaline derivative represented by the structural formula (103). Fig. 22 shows the structure of a light-emitting element 1, a light-emitting element 2, or a comparative light-emitting element 3. Fig. Figure 23 shows the current density-luminance characteristics of the light-emitting element 1, the light-emitting element 2, and the comparison light-emitting element 3. Fig. Figure 24 shows the voltage-luminance characteristics of the light-emitting element 1, the light-emitting element 2, and the comparison light-emitting element 3. Fig. 25 shows the luminance-power efficiency characteristics of the light-emitting element 1, the light-emitting element 2, and the comparative light-emitting element 3. Fig. 26 shows the voltage-current characteristics of the light-emitting element 1, the light-emitting element 2, and the comparison light-emitting element 3. Fig. 27 shows the emission spectra of the light-emitting element 1, the light-emitting element 2 and the comparative light-emitting element 3. Fig. 28A and Fig. 28B show the reliability of the light-emitting element 1, the light-emitting element 2, and the comparative light-emitting element 3. Fig. Figure 29 shows the current density-luminance characteristics of a light-emitting element 4. Fig. 30 shows the voltage-luminance characteristics of the light-emitting element 4. Fig. 31 shows the luminance-current efficiency characteristics of the light-emitting element 4. Fig. 32 shows the voltage-current characteristics of the light-emitting element 4. Fig. 33 shows the emission spectrum of the light-emitting element 4. Fig. 34A and Fig. 34B show the reliability of the light-emitting element 4. Fig. 35A and Fig. 35B are 1 H-NMR diagrams of a dibenzo[f,h]quinoxaline derivative represented by the structural formula (122). Fig. 36 shows the current density-luminance characteristics of a light-emitting element 5, a comparison light-emitting element 6, and a comparison light-emitting element 7. Fig. 37 shows the voltage-luminance characteristics of the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7. Fig. 38 shows the luminance-current efficiency characteristics of the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7. Fig. 39 shows the voltage-current characteristics of the light-emitting element 5, the comparison light-emitting element 6, and the comparison light-emitting element 7. Fig. 40 shows the emission spectra of the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7. Fig. 41A and Fig. 41B show the reliability of the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7. Fig. Figure 42 shows the current density-luminance characteristics of a light-emitting element 8. Fig. 43 shows the voltage-luminance characteristics of the light-emitting element 8. Fig. 44 shows the luminance-current efficiency characteristics of the light-emitting element 8. Fig. Figure 45 shows the voltage-current characteristics of the light-emitting element 8. Fig. 46 shows the emission spectrum of the light-emitting element 8. Fig. Figure 47 shows the voltage-current characteristics of a light-emitting element 1A after a preservation test. Fig. Figure 48 shows the luminance-external quantum efficiency characteristics of the light-emitting element 1A after the preservation test. Fig. Figure 49 shows the voltage-current characteristics of a light-emitting element 2A after a preservation test. Fig. Figure 50 shows the luminance-external quantum efficiency characteristics of the light-emitting element 2A after the preservation test. Fig. Figure 51 shows the voltage-current characteristics of a comparative light-emitting element 3A after a preservation test. Fig. Figure 52 shows the luminance-external quantum efficiency characteristics of the comparative light-emitting element 3A after the preservation test. Fig. 53 shows the voltage-current characteristics of a light-emitting element 4A after a preservation test. Fig. Figure 54 shows the luminance-external quantum efficiency characteristics of the light-emitting element 4A after the preservation test. Fig. 55 shows the voltage-current characteristics of a light-emitting element 8A after a preservation test. Fig. Figure 56 shows the luminance-external quantum efficiency characteristics of the light-emitting element 8A after the preservation test. Detailed description of the invention

[0026] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the following description, and its forms and details can be modified in various ways without departing from the spirit and scope of the present invention. Accordingly, the present invention should not be construed as being limited to the contents of the following embodiments.

[0027] It should be noted that the terms "film" and "layer" may be interchangeable depending on the situation or circumstances. For example, in some cases, the term "conductive layer" may be converted to the term "conductive film." Furthermore, in some cases, the term "insulating film" may be converted to the term "insulating layer." (Embodiment 1)

[0028] In this embodiment, a light-emitting element which is an embodiment of the present invention will be described.

[0029] In a light-emitting element described in this embodiment, an EL layer including a light-emitting layer is provided between a pair of electrodes (a first electrode (anode) and a second electrode (cathode)), and the EL layer includes, in addition to the light-emitting layer, a hole-injection layer, a hole-transport layer, an electron-transport layer, an electron-injection layer, and the like.

[0030] When a voltage is applied to the light-emitting element, holes injected from the first electrode side and electrons injected from the second electrode side recombine in the light-emitting layer; with the energy generated by the recombination, a light-emitting substance contained in the light-emitting layer emits light.

[0031] As in Fig. As shown in Figure 1, a light-emitting layer 100 includes a first organic compound (h) 101 having an electron-transport property and a hole-transport property, a second organic compound (a) 102 having a hole-transport property, and a light-emitting substance (not shown in the drawing). Note that the combination of the first organic compound (h) 101 and the second organic compound (a) 102 forms an excited complex (also called an exciplex). This means: The lowest unoccupied molecular orbital (LUMO) level of the first organic compound (h) 101 is at least lower than the LUMO level of the second organic compound (a) 102, and the highest occupied molecular orbital (HOMO) level of the first organic compound (h) 101 is at least lower than the HOMO level of the second organic compound (a) 102.Accordingly, as shown in the figure, the excitation energy of the generated exciplex is determined by an energy difference (i.e., ΔE. e in the drawing) between the LUMO level of the first organic compound (h) 101 (LUMO (h)) and the HOMO level of the second organic compound (a) 102 (HOMO (a)).

[0032] Such a light-emitting layer 100 enables energy transfer by utilizing an overlap between the emission spectrum of the exciplex and the absorption spectrum of the light-emitting substance (guest material), resulting in high energy transfer efficiency; therefore, a light-emitting element with high external quantum efficiency can be achieved. Furthermore, an electrical energy (i.e., a voltage) corresponding to ΔE e is required for the exciplex to be electrically excited. This energy ΔE e is less than an energy ΔE h, which is necessary for the electrical excitation of the first organic compound (h) 101, and an energy ΔE a , which is necessary for the electrical excitation of the second organic compound (a) 102. In other words, with such a light-emitting layer 100, the operating voltage (the emission start voltage) of the light-emitting element can be reduced.

[0033] Without using the first organic compound (h) 101 and the second organic compound (a) 102, a kind of organic compound having a HOMO-LUMO gap, the ΔE ecan be used for a light-emitting layer, whereby the operating voltage (emission start voltage) can be achieved that is as low as in the case of the light-emitting layer 100. However, in the case of using a type of organic compound, the triplet excitation energy is much lower than the singlet excitation energy; therefore, it is difficult to achieve light emission by transferring the triplet excitation energy to a light-emitting substance (a guest material). In contrast, in the exciplex, the singlet excitation energy and the triplet excitation energy are at substantially the same level, which allows both the singlet excitation energy and the triplet excitation energy to be transferred to the light-emitting substance.As a result, in addition to the above-described effect of voltage reduction, higher efficiency can be achieved in the light-emitting element. A detailed mechanism for this higher efficiency is described below.

[0034] When the light-emitting substance is a phosphorescent compound, both the singlet excitation energy and the triplet excitation energy of the exciplex are transferred to the triplet excited state of the phosphorescent compound, and light emission from the triplet excited state (i.e., phosphorescence) is achieved; therefore, the light-emitting substance is best used as a phosphorescent compound to achieve higher efficiency.

[0035] When the light-emitting substance is a thermally activated, delayed-fluorescence compound, the singlet excitation energy of the exciplex is transferred to the singlet excited state of the light-emitting substance, and light emission from the singlet excited state (i.e., fluorescence) is achieved. Furthermore, the triplet excitation energy of the exciplex is transferred to the triplet excited state of the light-emitting substance; however, due to thermal activation, reverse intersystem crossing occurs from part or all of the triplet excited state to the singlet excited state of the light-emitting substance, thereby yielding fluorescence, resulting in higher efficiency.

[0036] When the light-emitting substance is a fluorescent compound, the singlet excitation energy of the exciplex is transferred to the singlet excited state of the light-emitting substance, and light emission from the singlet excited state (i.e., fluorescence) is achieved. Conversely, the triplet excitation energy of the exciplex is transferred to the triplet excited state of the light-emitting substance and thermally deactivated; therefore, it appears that no higher efficiency can be achieved. However, the exciplex, which is an energy donor, has a small difference between the singlet excitation energy and the triplet excitation energy and thus emits thermally activated, delayed fluorescence itself.In other words, in the exciplex, reverse intersystem crossing occurs from part of the triplet excited state or from the entire triplet excited state to the singlet excited state, so that the proportion of singlet excitons is higher than in the normal situation. The proportion of singlet excitons in the exciplex, which is an energy donor, is high, and the singlet excitation energy of the exciplex is transferred to the singlet excited state of the light-emitting substance, thus achieving high emission efficiency even when a fluorescent compound is used as the light-emitting substance. This phenomenon is also a feature of the present invention.

[0037] As described above, a light-emitting element in which an exciplex in a light-emitting layer serves as an energy donor is effective in all cases where a phosphorescent compound, a thermally activated delayed fluorescent compound, and a fluorescent compound are used as a light-emitting substance, but there is a problem in controlling a light-emitting region.

[0038] As already described above, the following condition is required to form the exciplex of the first organic compound (h) 101 and the second organic compound (a) 102: the LUMO level of the first organic compound (h) 101 (LUMO(h)) is at least lower than the LUMO level of the second organic compound (a) 102 (LUMO(a)), and the HOMO level of the first organic compound (h) 101 (HOMO(h)) is at least lower than the HOMO level of the second organic compound (a) 102 (HOMO(a)). Specifically, in a conventional light-emitting element in which an exciplex in the light-emitting layer 100 serves as an energy donor, an energy difference ΔE HOMObetween the HOMO level of the first organic compound (h) 101 (HOMO(h)) and the HOMO level of the second organic compound (a) 102 (HOMO(a)) is very large, forming an exciplex. For example, 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II) is used as the first organic compound (h) 101, and N-(1,1'-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine (abbreviation: PCBBiF) is used as the second organic compound (a) 102; in this case, the HOMO level of the first organic compound (h) 101 (HOMO(h)) is -6.22 eV, the HOMO level of the second organic compound (a) 102 (HOMO(a)) is -5.36 eV, and ΔE HOMO is as much as 0.86 eV.

[0039] If, as described above, a difference (ΔE HOMO) between the HOMO level of the first organic compound (h) 101 (HOMO(h)) and the HOMO level of the second organic compound (a) 102 (HOMO(a)) is large, the charge carrier balance tends to change greatly depending on the amount of the second organic compound (a) 102 in the light-emitting layer 100. That is, too small an amount of the second organic compound (a) (102) results in excess electrons, and a light-emitting region thus exists mainly on the anode side; conversely, the amount of the second organic compound (a) (102) that only slightly exceeds the optimal amount results in excess holes, and the holes are transported to the cathode side.In such a narrow-range device, even if the first organic compound (h) 101 and the second organic compound (a) 102 are mixed in an optimal ratio, a small change in the carrier balance caused by long-term operation leads to a decrease in recombination efficiency and lower luminance. When ΔE. HOMO is large, holes are accumulated in the second organic compound (a) 102, so that the recombination area in the light-emitting layer 100 is reduced. In the case where the recombination area in the light-emitting layer 100 is large, the entire light-emitting layer 100 can be used, and the reliability is high.

[0040] Due to deterioration of an electron injection electrode (cathode) or the like, the electron injection property of the light-emitting element decreases, which may cause the recombination region to shift to the cathode side due to long-term operation. In this case, the average distance for transporting holes to the recombination region becomes longer; therefore, if the light-emitting layer 100 has insufficient hole transport property, the resistance of the light-emitting element increases. In other words, in the case where the element is operated at a constant current, the operating voltage increases greatly over time. If the difference (ΔE HOMO) between the HOMO level of the first organic compound (h) (HOMO(h)) and the HOMO level of the second organic compound (a) (HOMO(a)) is large, holes are difficult to transport through the light-emitting layer 100; thus, an increase in the operating voltage over time is very problematic.

[0041] An embodiment of the present invention solves a problem in the above-described light-emitting element in which the exciplex in the light-emitting layer 100 serves as an energy donor. That is, a light-emitting element embodying the present invention includes an EL layer between an anode and a cathode.The EL layer includes the light-emitting layer 100; the light-emitting layer 100 contains the first organic compound (h) 101 having an electron-transport property and a hole-transport property, the second organic compound (a) 102 having a hole-transport property, and the light-emitting substance; the combination of the first organic compound (h) 101 and the second organic compound (a) 102 forms an exciplex; the HOMO level of the first organic compound (h) (HOMO(h)) is lower than the HOMO level of the second organic compound (a) (HOMO(a)); and a difference between the HOMO level of the first organic compound (h) (HOMO(h)) and the HOMO level of the second organic compound (a) (HOMO(a)) is less than or equal to 0.4 eV.

[0042] With such a structure, holes are injected not only into the second organic compound (a) 102 but also partially into the first organic compound (h) 101. As a result, holes are unlikely to accumulate in the second organic compound (a) 102; therefore, a light-emitting element can be obtained in which the carrier balance can be easily maintained and the recombination range in the light-emitting layer 100 is large. Furthermore, a voltage increase can be suppressed by long-term operation (constant current operation).In the above case, recombination occurs in the first organic compound (h) 101 in a portion of the light-emitting layer 100, resulting in the formation of an excited state of the first organic compound, but this state is quickly converted into an exciplex; therefore, higher efficiency can be achieved using the exciplex. Furthermore, the effect of reducing the operating voltage (the emission start voltage) can be maintained because holes are mainly injected into the second organic compound (a) 102.

[0043] In this way, ΔE HOMOis set to less than or equal to 0.4 eV (and greater than 0 eV), and the combination of the first organic compound (h) 101 and the second organic compound (a) 102 forms an exciplex, which can solve the above problem. Since holes are injected not only into the second organic compound (a) 102 but also into the first organic compound (h) 101, ΔE HOMO preferably less than or equal to 0.3 eV.

[0044] Compounds suitable for achieving the above concept are as follows. The first organic compound (h) 101 has a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, and preferably does not have a triarylamine skeleton. The six-membered nitrogen-containing heteroaromatic ring is pyrazine, pyridazine, triazine, or tetrazine, and / or a benzene ring is condensed with the six-membered nitrogen-containing heteroaromatic ring. That is, a compound that has an electron-transport property due to a six-membered nitrogen-containing heteroaromatic ring and has a moderate hole-transport property due to a carbazole skeleton and no triarylamine skeleton is preferably used.The second organic compound (a) 102 has a hole transport property and preferably has a triarylamine framework such that the HOMO level of the second organic compound (a) 102 is higher than that of the first organic compound (h) 101.

[0045] A compound having a triarylamine skeleton often has a HOMO level of about -5.5 eV, or higher than or equal to -5.5 eV, according to cyclic voltammetry (CV) measurement, while the HOMO level of a simple 9-phenylcarbazole is -5.88 eV, so the difference between the HOMO level of the compound having a triarylamine skeleton and that of 9-phenylcarbazole is often greater than or equal to 0.4 eV. Therefore, in one embodiment of the present invention, the first organic compound (h) 101 preferably has a bicarbazole skeleton as the carbazole skeleton, since the HOMO level of bicarbazole is higher than that of 9-phenylcarbazole. In particular, in one embodiment of the present invention, a 3,3'-bicarbazole skeleton or a 2,3'-bicarbazole skeleton is preferably introduced into the first organic compound (h) 101 because its HOMO level is about -5.6 eV to -5.7 eV.

[0046] When a benzene ring is fused with the six-membered nitrogen-containing heteroaromatic ring, examples of the six-membered nitrogen-containing heteroaromatic ring include, in addition to pyridine, diazine, such as pyrazine, pyrimidine, or pyridazine, triazine, and tetrazine. Examples of the six-membered nitrogen-containing heteroaromatic ring fused with a benzene ring include quinoline, isoquinoline, and dibenzo[f,h]quinoline. Furthermore, naphthyridine, such as typically quinoxaline, quinazoline, and phthalazine, dibenzo[f,h]quinoxaline, dibenzo[f,h]quinazoline, and the like, can also be used.

[0047] In one embodiment of the present invention, as described above, holes are preferably injected and transported not only into the second organic compound (a) 102, but also into the first organic compound (h) 101. Therefore, as in Fig. 2, preferably, a third organic compound (p) 105 having a hole transport property is used for a hole transport layer 104 in contact with the light-emitting layer 100, and the HOMO level of the third organic compound (p) 105 (HOMO(p)) is set lower than the HOMO level of the second organic compound (a) 102 (HOMO(a)) in order to improve a hole injection property over both the first organic compound (h) 101 and the second organic compound (a) 102 in the light-emitting layer 100. In particular, the third organic compound (p) 105 is preferably selected such that the HOMO level of the third organic compound (p) 105 (HOMO(p)) can be a level between the HOMO level of the second organic compound (a) 102 (HOMO(a)) and the HOMO level of the first organic compound (h) 101 (HOMO(h)).

[0048] A concrete example of a light-emitting element which is an embodiment of the present invention and has the above structure will be explained with reference to Fig. 3A and Fig. 3B described below.

[0049] For a first electrode (anode) 201 and a second electrode (cathode) 203, a metal, an alloy, an electrically conductive compound, a mixture of these, and the like can be used. Specifically, indium oxide-tin oxide (indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (indium zinc oxide), indium oxide containing tungsten oxide and zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), and titanium (Ti) can be used. Furthermore, an element belonging to group 1 or 2 of the periodic table, for example, an alkali metal such as lithium (Li) or cesium (Cs), an alkaline earth metal such as Ni, or an alkaline earth metal such as Ni, can be used. B. Calcium (Ca) or Strontium (Sr), Magnesium (Mg), an alloy containing such an element (MgAg, AlLi), a rare earth metal, such asEuropium (Eu) or ytterbium (Yb), an alloy containing such an element, graphene, and the like can be used. The first electrode (anode) 201 and the second electrode (cathode) 203 can be formed, for example, by a sputtering method, an evaporation method (including a vacuum evaporation method), or the like.

[0050] A hole-injection layer 211 injects holes into a light-emitting layer 213 via a hole-transport layer 212 with a high hole-transport property and contains a substance with a high hole-transport property (also called a hole-transport compound) and an acceptor substance. The hole-injection layer 211 contains a substance with a high hole-transport property and an acceptor substance, so that electrons are extracted from the substance with a high hole-transport property by the acceptor substance to generate holes, and the holes are injected into the light-emitting layer 213 via the hole-transport layer 212. The hole-transport layer 212 is formed using a substance with a high hole-transport property.

[0051] Examples of the substance having a high hole transport property used for the hole injection layer 211 and the hole transport layer 212 include aromatic amine compounds such as: B. 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4',4''-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), 4,4',4''-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA), 4,4',4''-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA) and 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB); 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1); 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2); and 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1).Alternatively, the following carbazole derivatives and the like can be used: 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA). The substances mentioned here are mainly substances with a hole mobility greater than or equal to 1 × 10. -6 cm 2 / Vs. It should be noted that other substances can also be used as long as the substances have hole transport properties that are higher than electron transport properties.

[0052] Alternatively, high molecular weight compounds such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA) and poly[N,N'-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can be used.

[0053] Examples of the acceptor substance used for the hole-injection layer 211 include oxides of metals belonging to groups 4 to 8 of the periodic table. In particular, molybdenum oxide is particularly preferred.

[0054] The light-emitting layer 213 is a layer containing a light-emitting substance. When the light-emitting layer 213 contains the Fig. 1, the light-emitting layer 213 contains a first organic compound having an electron-transport property and a hole-transport property, which will be described later, a second organic compound having a hole-transport property, which has been described above, and a light-emitting substance. The combination of the first organic compound and the second organic compound forms an exciplex (also called an excited complex) during the recombination of charge carriers (electrons and holes) in the light-emitting layer. When the exciplex is formed in the light-emitting layer, the fluorescence spectrum of the first organic compound and that of the second organic compound are converted into the emission spectrum of the exciplex, which is on the longer wavelength side.Furthermore, energy transfer from the singlet excited state can be maximized if the first organic compound and the second organic compound are selected such that the emission spectrum of the exciplex largely overlaps the absorption spectrum of a guest material. It is assumed that even in the case of the triplet excited state, energy transfer occurs from the exciplex, not from a host material.

[0055] Although the combination of the first organic compound and the second organic compound can be determined to form an exciplex, a combination of a compound that readily accepts electrons (a compound having an electron-trapping property) and a compound that readily accepts holes (a compound having a hole-trapping property) is preferably used. The first organic compound is preferably capable of trapping (or transporting) not only electrons but also holes, and therefore preferably has a six-membered nitrogen-containing heteroaromatic ring and a bicarbazole skeleton, and does not have a triarylamine skeleton. For example, a compound represented by the following general formula (G0) is preferably used.

[0056] In the formula, A represents a dibenzo[f,h]quinoxalinyl group; R 1 to R 15independently represent hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group.

[0057] If Ar contains an anthracenylene group, the triplet excitation energy of the compound is significantly reduced (to an energy less than or equal to 1.7 eV), in which case the triplet excitation energy of the exciplex could be quenched. Therefore, it is preferable for an arylene group in Ar not to contain an anthracenylene group.

[0058] In particular, the compounds represented by the general formulas (G1) to (G3) are preferably used. Specifically, 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2PCCzPDBq), 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[F,h]quinoxaline (abbreviation: 2mPCCzPDBq), 2-{4-[2-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[F,h]quinoxaline (abbreviation: 2PCCzPDBq-02) and 2-{3-[2-(N-Phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[F,h]quinox aline (abbreviation: 2mPCCzPDBq-02) can be used.

[0059] Examples of the compound that easily accepts holes include compounds with triarylamine skeletons, such as: B. 4-Phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 3-[N-(1-Naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), 4,4',4''-Tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation: 1'-TNATA), 2,7-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9'-bifluorene (abbreviation: DPA2SF), N,N'-Bis(9-phenylcarbazol-3-yl)-N,N'-diphenylbenzene-1,3-diamine (abbreviation: PCA2B), N-(9,9-Dimethyl-2-N',N'-diphenylamino-9H-fluoren-7-yl)diphenylamine (abbreviation: DPNF), N,N',N''-Triphenyl-N,N',N''-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine (abbreviation: PCA3B), 2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9'-bifluorene (abbreviation: PCASF), 2-[N-(4-Diphenylaminophenyl)-N-phenylamino]spiro-9,9'-bifluorene (abbreviation: DPASF), N,N'-Bis[4-(carbazol-9-yl)phenyl]-N,N'-diphenyl-9,9-dimethylfluorene-2,7-diamine (abbreviation: YGA2F), 4,4'-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD), 4,4'-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), N-(9,9-Dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N'-phenyl-N'-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviation: DFLADFL), 3-[N-(9-Phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3-[N-(4-Diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA1), 3,6-Bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA2), 4,4'-Bis(N-{4-[N'-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviation: DNTPD), 3,6-Bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviation: PCzTPN2) and 3,6-Bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2).

[0060] The first organic compound and the second organic compound are not limited to the above examples, as long as the combination of the first organic compound and the second organic compound can form an exciplex, the emission spectrum of the exciplex overlaps the absorption spectrum of the light-emitting substance, and the peak of the emission spectrum of the exciplex has a longer wavelength than the peak of the absorption spectrum of the light-emitting substance.

[0061] It should be noted that when the electron-absorbing compound and the hole-absorbing compound are used as the first organic compound and the second organic compound, the carrier balance can be controlled by the mixing ratio of the compounds. Specifically, the ratio of the first organic compound to the second organic compound is preferably 1:9 to 9:1.

[0062] As materials that can be used as the light-emitting substance and the emission center substance in the light-emitting layer 213, a light-emitting substance that converts singlet excitation energy into light emission, a light-emitting substance that converts triplet excitation energy into light emission, and the like can be used independently or in combination. Examples of the light-emitting substance and the emission center substance are described below.

[0063] As an example of the light-emitting substance that converts the singlet excitation energy into light emission, a substance that emits fluorescence (a fluorescent compound) can be given.

[0064] Examples of the substance that emits fluorescence include N,N'-bis[4-(9H-carbazol-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine (abbreviation: YGA2S), 4-(9H-carbazol-9-yl)-4'-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), 4-(9H-carbazol-9-yl)-4'-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (abbreviation: TBP), 4-(10-Phenyl-9-anthryl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPA), N,N''-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N',N'-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9-Diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-Diphenyl-2-anthryl)phenyl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N',N',N'',N'',N''',N''-Octaphenyldibenzo[g,p]chrysen-2,7,10,15-tetraamine (abbreviation: DBC1), coumarin 30, N-(9,10-Diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCAPA), N-[9,10-Bis(1,1'-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCABPhA), N-(9,10-Diphenyl-2-anthryl)-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-Bis(1,1'-biphenyl-2-yl)-2-anthryl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA), 9,10-Bis(1,1'-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracene-2-amine (abbreviation: 2YGABPhA), N,N,9-Triphenylanthracene-9-amine (abbreviation: DPhAPhA), Coumarin 545T, N,N'-Diphenylquinacridone (abbreviation: DPQd), Rubrene, 5,12-Bis(1,1'-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), 2-(2-{2-[4-(Dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propane-1-nitrile (abbreviation: DCM1), 2-{2-Methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N',N'-Tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,14-Diphenyl-N,N,N',N'-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD), {2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoliz in-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), {2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoliz in-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (Abbreviation: DCJTB), 2-(2,6-Bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM) and 2-{2,6-Bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]c hinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM).

[0065] Examples of light-emitting substances that convert triplet excitation energy into light emission include phosphorescent substances (phosphorescent compounds) and thermally activated delayed fluorescent (TADF) materials that emit thermally activated delayed fluorescence. Note that delayed fluorescence, which TADF materials exhibit, refers to light emission that has the same spectrum as normal fluorescence and a very long lifetime. The lifetime is 10 -6 seconds or longer, preferably 10 -3 seconds or longer.

[0066] Examples of the substance that emits phosphorescence include bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinato-N,C 2'}iridium(III)picolinate (abbreviation: Ir(CF3ppy)2(pic)), bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2']iridium(III)acetylacetonate (abbreviation: FIracac), tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)3), bis(2-phenylpyridinato)iridium(III)acetylacetonate (abbreviation: Ir(ppy)2(acac)), tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: Tb(acac)3(Phen)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)2(acac)), bis(2,4-diphenyl-1,3-oxazolato-N,C 2' )iridium(III)acetylacetonate (abbreviation: Ir(dpo)2(acac)), bis{2-[4'-(perfluorophenyl)phenyl]pyridinato-N,C 2'}iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)2(acac)), bis(2-phenylbenzothiazolato-N,C 2' )iridium(III)acetylacetonate (abbreviation: Ir(bt)2(acac)), bis[2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C 3' ]iridium(III)acetylacetonate (abbreviation: Ir(btp)2(acac)), bis(1-phenylisoquinolinato-N,C 2')iridium(III)acetylacetonate (abbreviation: Ir(piq)2(acac)), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq)2(acac)), (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-Me)2(acac)]), (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-iPr)2(acac)]), (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium (III) (abbreviation: Ir(tppr)2(acac)), Bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin-platinum(II) (abbreviation: PtOEP), tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)3(Phen)) and Tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)3(Phen)).

[0067] Examples of TADF materials include fullerene, a derivative thereof, an acridine derivative such as proflavin, and eosin. Other examples include a metal-containing porphyrin, such as porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd). Examples of the metal-containing porphyrin include a protoporphyrin-tin fluoride complex (SnF2(Proto IX)), a mesoporphyrin-tin fluoride complex (SnF2(Meso IX)), a hematoporphyrin-tin fluoride complex (SnF2(Hemato IX)), a coproporphyrin-tetramethyl ester-tin fluoride complex (SnF2(Copro III-4Me)), an octaethylporphyrin-tin fluoride complex (SnF2(OEP)), an etioporphyrin-tin fluoride complex (SnF2(Etio I)), and an octaethylporphyrin-platinum chloride complex (PtCl2(OEP)).Alternatively, a heterocyclic compound containing a π-electron-rich heteroaromatic ring and a π-electron-poor heteroaromatic ring can be used, for example, 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (PIC-TRZ). Note that a substance in which the π-electron-rich heteroaromatic ring is directly bonded to the π-electron-poor heteroaromatic ring is particularly preferred because both the donor property of the π-electron-rich heteroaromatic ring and the acceptor property of the π-electron-poor heteroaromatic ring are enhanced, and the energy difference between the S1 level and the T1 level is reduced.

[0068] The light-emitting layer 213 may have a multilayer structure as shown in Fig. 3B. In this case, each layer in the multilayer structure emits light. For example, fluorescence is obtained from a first light-emitting layer 213 (a1), and phosphorescence is obtained from a second light-emitting layer 213 (a2) arranged above the first layer. Note that the order of the arranged layers may be reversed. Preferably, light emission due to energy transfer from an exciplex to a dopant is obtained from the layer emitting phosphorescence. In the case where blue light emission is obtained from one of the first and second layers, orange or yellow light emission may be obtained from the other layer. Each layer may also contain multiple types of dopants.

[0069] An electron-transport layer 214 is a layer containing a substance with a high electron-transport property (also called an electron-transport compound). A metal complex such as tris(8-quinolinolato)aluminum(III) (abbreviation: Alq3), tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq3), bis(10-hydroxybenzo[h]quinolinolato)beryllium(II) (abbreviation: BeBq2), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis[2-2-hydroxyphenyl)benzoxazolato]zinc(II) (abbreviation: Zn(BOX)2), or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc(II) (abbreviation: Zn(BTZ)2) can be used for the electron-transport layer 214. Alternatively, a heteroaromatic compound such as2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4'-tert-butylphenyl)-4-phenyl-5-(4''-biphenyl)-1,2,4-triazole (abbreviation: TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP) or 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can be used. Alternatively, a high-molecular-weight compound such as poly(2,5-pyridinediyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), or poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy) can be used. The substances mentioned here are mainly substances with an electron mobility greater than or equal to 1 × 10. -6 cm 2 / Vs. It should be noted that other substances can also be used for the electron transport layer 214 as long as the substances have electron transport properties that are higher than hole transport properties.

[0070] The electron transport layer 214 is not limited to a single layer and may have a multilayer structure including two or more layers containing any of the above-mentioned substances.

[0071] An electron injection layer 215 is a layer containing a substance with a high electron injection property. The electron injection layer 215 can be formed using an alkali metal, an alkaline earth metal, or their compound, such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), or lithium oxide (LiO). x). Alternatively, a rare earth metal compound such as erbium fluoride (ErF3) may be used. Alternatively, an electride may be used for the electron injection layer 215. Examples of the electride include a substance in which electrons are added at a high concentration to calcium oxide-aluminum oxide. Any of the substances for forming the electron transport layer 214 mentioned above may also be used.

[0072] The electron-injection layer 215 can also be formed using a composite material in which an organic compound and an electron donor are mixed. The composite material has excellent electron-injection properties and electron-transport properties because electrons are generated in the organic compound by the electron donor. In this case, a material that can efficiently transport the generated electrons is preferably used as the organic compound. For example, one of the above substances (such as a metal complex or a heteroaromatic compound) can be used to form the electron-transport layer 214. A substance that has an electron-donating property with respect to the organic compound can be used as the electron donor.In particular, an alkali metal, an alkaline earth metal, and a rare earth metal are preferred, and lithium, cesium, magnesium, calcium, erbium, ytterbium, and the like can be cited. Furthermore, an alkali metal oxide or an alkaline earth metal oxide is preferred, and, for example, lithium oxide, calcium oxide, barium oxide, and the like can be cited. Alternatively, a Lewis base such as magnesium oxide can be used. An organic compound such as tetrathiafulvalene (abbreviation: TTF) can also be used.

[0073] Note that the hole injection layer 211, the hole transport layer 212, the light-emitting layer 213, the electron transport layer 214, and the electron injection layer 215 mentioned above can each be formed by a method such as an evaporation method (including a vacuum evaporation method), an inkjet method, or a coating method.

[0074] In the above light-emitting element, holes and electrons recombine in the EL layer 202, thereby emitting light. This emitted light is extracted to the outside through the first electrode 201 and / or the second electrode 203. Therefore, the first electrode 201 and / or the second electrode 203 is an electrode with a light-transmitting property.

[0075] The light-emitting element described in this embodiment enables energy transfer by utilizing an overlap between the emission spectrum of the exciplex and the absorption spectrum of a phosphorescent compound (a guest material), resulting in high energy transfer efficiency; therefore, a light-emitting element with high external quantum efficiency can be achieved.

[0076] It should be noted that the structure described in this embodiment may be combined with any of the structures described in the other embodiments as needed. (Embodiment 2)

[0077] In this embodiment, a dibenzo[f,h]quinoxaline derivative which can be used in a light-emitting element according to the present invention is described.

[0078] A dibenzo[f,h]quinoxaline derivative is represented by the following general formula (G0).

[0079] In the formula, A represents a dibenzo[f,h]quinoxalinyl group; R 1 to R 15 independently represent hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group.

[0080] The dibenzo[f,h]quinoxaline derivative represented by the general formula (G0) can be prepared by the following synthesis method. As shown in the following synthesis scheme (a), the dibenzo[f,h]quinoxaline derivative represented by the general formula (G0) can be prepared by reacting a halogen compound (A1) of a dibenzo[f,h]quinoxaline derivative with an arylboronic acid compound (A2) of a bicarbazole derivative.

[0081] In the formula, A represents a dibenzo[f,h]quinoxalinyl group; R 1 to R 15independently represent hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group. In addition, X represents a halogen. When Ar is a substituted or unsubstituted arylene group having 6 to 25 carbon atoms, B represents a boronic acid, a boronic ester, a cyclic triol borate salt, or the like. As the cyclic triol borate salt, a lithium salt, a potassium salt, or a sodium salt can be used. When Ar is a single bond, B represents hydrogen.

[0082] In addition, as shown in the following synthesis scheme (b), the dibenzo[f,h]quinoxaline derivative represented by the general formula (G0) can be prepared by obtaining an intermediate (B2) by a reaction of a halogen compound (A1) of a dibenzo[f,h]quinoxaline derivative with a halogen-substituted arylboronic acid (B1) and then reacting with a bicarbazole derivative (B3).

[0083] In the formula, A represents a dibenzo[f,h]quinoxalinyl group; R 1 to R 15independently represent hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 5 to 7 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted arylene group having 6 to 25 carbon atoms or a single bond. Preferably, an arylene group in Ar does not have an anthracenylene group. Additionally, X represents a halogen. B represents a boronic acid, a boronic ester, a cyclic triol borate salt, or the like.

[0084] When Ar in the general formula (G0) is a single bond, a halogen compound (A1) of a dibenzo[f,h]quinoxaline derivative reacts directly with a bicarbazole derivative (B3).

[0085] A dibenzo[f,h]quinoxaline derivative that can be prepared by any of the above synthesis methods is preferably a compound represented by any one of the above general formulas (G1) to (G3). Specific structural formulas of dibenzo[f,h]quinoxaline derivatives that are embodiments of the present invention and represented by the general formulas (G0) to (G3) are shown below (the following structural formulas (100) to (131)). Note that the present invention is not limited thereto.

[0086] A dibenzo[f,h]quinoxaline derivative is used in a light-emitting element of one embodiment of the present invention, whereby a light-emitting element, a light-emitting device, an electronic device, or a lighting device with high emission efficiency and high reliability can be provided. A light-emitting element, a light-emitting device, an electronic device, or a lighting device with low power consumption can also be obtained.

[0087] The dibenzo[f,h]quinoxaline derivative represented by any of the general formulas (G0) to (G3) exhibits electron-transport properties and hole-transport properties and can therefore be used as a host material of a light-emitting layer or for an electron-transport layer or a hole-transport layer. Furthermore, the dibenzo[f,h]quinoxaline derivative represented by any of the general formulas (G0) to (G3) emits fluorescence and can therefore be used as a light-emitting substance of a light-emitting element.As described above, the dibenzo[f,h]quinoxaline derivative represented by any one of the general formulas (G0) to (G3) is a useful novel compound that can be used in a light-emitting element as various materials; therefore, a light-emitting element containing the dibenzo[f,h]quinoxaline derivative represented by any one of the general formulas (G0) to (G3) is a light-emitting element that is an embodiment of the present invention.

[0088] It should be noted that the structure described in this embodiment may be combined with any of the structures described in the other embodiments as needed. (Embodiment 3)

[0089] In this embodiment, as a light-emitting element which is an embodiment of the present invention, a light-emitting element (hereinafter referred to as a tandem light-emitting element) including a plurality of EL layers with a charge generation layer provided therebetween is described. As shown in Fig. 4A, the tandem light-emitting element includes a plurality of EL layers (a first EL layer 402(1) and a second EL layer 402(2)) between a pair of electrodes (a first electrode 401 and a second electrode 404).

[0090] In this embodiment, the first electrode 401 serves as the anode, and the second electrode 404 serves as the cathode. The first electrode 401 and the second electrode 404 may have structures similar to those of Embodiment 1. All or any of the plurality of EL layers (the first EL layer 402(1) and the second EL layer 402(2)) may have structures similar to those of Embodiment 1. In other words, the structures of the first EL layer 402(1) and the second EL layer 402(2) may be the same or different from each other, and they may be similar to those of Embodiment 1. The dibenzo[f,h]quinoxaline derivative described in Embodiment 2 may be used for any of the plurality of EL layers (the first EL layer 402(1) and the second EL layer 402(2)).

[0091] A charge generation layer 405 is provided between the plurality of EL layers (the first EL layer 402(1) and the second EL layer 402(2)). The charge generation layer 405 has a function of injecting electrons into one of the EL layers and injecting holes into the other of the EL layers when a voltage is applied between the first electrode 401 and the second electrode 404. In this embodiment, when a voltage is applied such that the potential of the first electrode 401 is higher than that of the second electrode 404, the charge generation layer 405 injects electrons into the first EL layer 402(1) and holes into the second EL layer 402(2).

[0092] The charge generation layer 405 preferably has a visible light transmittance in terms of light extraction efficiency (specifically, the charge generation layer 405 has a visible light transmittance greater than or equal to 40%). Furthermore, the charge generation layer 405 operates even if it has a lower conductivity than the first electrode 401 or the second electrode 404.

[0093] The charge generation layer 405 may have either a structure in which an electron acceptor of an organic compound with a high hole-transport property is added, or a structure in which an electron donor of an organic compound with a high electron-transport property is added. Alternatively, both of these structures may be arranged one above the other.

[0094] In the case of the structure in which an electron acceptor is added to an organic compound with a high hole-transport property, an aromatic amine compound such as NPB, TPD, TDATA, MTDATA, or 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), or the like, can be used as the organic compound with a high hole-transport property. The substances mentioned here are mainly substances with a hole mobility of greater than or equal to 1 × 10 -6 cm 2 / Vs. It should be noted that other substances can also be used as long as the substances have hole transport properties that are higher than electron transport properties.

[0095] Electron acceptors include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, and the like. Transition metal oxides can also be used. Oxides of metals belonging to groups 4 to 8 of the periodic table can also be used. In particular, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferably used due to their high electron acceptor properties. Molybdenum oxide is particularly preferred because of its stability in air, low hygroscopicity, and ease of handling.

[0096] On the other hand, in the case of the structure in which an electron donor is added to an organic compound with a high electron-transport property, a metal complex having a quinoline skeleton or a benzoquinoline skeleton, such as Alq3, Almq3, BeBq2, or BAlq, or the like, can be used as the organic compound with a high electron-transport property. Alternatively, a metal complex having an oxazole-based ligand or a thiazole-based ligand, such as Zn(BOX)2 or Zn(BTZ)2, can be used. Alternatively, in addition to such a metal complex, PBD, OXD-7, TAZ, BPhen, BCP, or the like can be used. The substances mentioned here are mainly substances with an electron mobility of greater than or equal to 1 × 10 -6 cm 2 / Vs. It should be noted that other substances can also be used as long as the substances have electron transport properties that are higher than hole transport properties.

[0097] An alkali metal, an alkaline earth metal, a rare earth metal, a metal belonging to Group 2 or 13 of the Periodic Table, or an oxide or carbonate thereof can be used as the electron donor. In particular, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or the like is preferably used. Alternatively, an organic compound such as tetrathianaphthacene can be used as the electron donor.

[0098] Note that forming the charge generation layer 405 using any of the materials described above can suppress an increase in the operating voltage caused by the stacking of the EL layers.

[0099] Although in this embodiment the light-emitting element having two EL layers is described, the present invention can be similarly applied to a light-emitting element in which, as shown in Fig. 4B, n EL layers (402(1) to 402(n)) (n is three or more) are stacked. In the case where, as in the light-emitting element of this embodiment, a plurality of EL layers are arranged between a pair of electrodes, by providing charge generation layers (405(1) to 405(n-1)) between the EL layers, light emission in a high luminance range can be obtained while keeping the current density low. Since the current density can be kept low, the element can have a long lifetime.Further, when the light-emitting element is applied to a light-emitting device, an electronic device, a lighting device, and the like, each having a large light-emitting area, a voltage drop due to the resistance of an electrode material can be reduced, thereby achieving uniform light emission in a large area.

[0100] When the EL layers have different emission colors, a desired emission color can be obtained from the light-emitting element as a whole. For example, in the light-emitting element having two EL layers, when an emission color of a first EL layer and an emission color of a second EL layer are set to be complementary colors, a light-emitting element that emits white light as a whole can be obtained. Note that "complementary color" refers to a relationship between colors in which an achromatic color is obtained when they are mixed. In other words, when lights that are complementary to each other are mixed, white light emission can be obtained.Specifically, as an example, a combination is given in which blue light emission is obtained from the first EL layer and yellow (or orange) light emission is obtained from the second EL layer. In this case, it is unnecessary for both blue light emission and yellow (or orange) light emission to be fluorescence or phosphorescence. For example, a combination in which blue light emission is fluorescence and yellow (orange) light emission is phosphorescence, or a combination in which blue light emission is phosphorescence and yellow (orange) light emission is fluorescence may be used. Furthermore, a multilayer structure suitable for adjusting an optical path length of the light-emitting element (e.g.,a structure in which a first light-emitting layer has yellow light emission and a second light-emitting layer has blue light emission) is preferably used, whereby the element properties can be further improved.

[0101] For example, even in a light-emitting element having three EL layers, white light emission can be similarly obtained from a light-emitting element as a whole when an emission color of a first EL layer is red, an emission color of a second EL layer is green, and an emission color of a third EL layer is blue.

[0102] It should be noted that the structure described in this embodiment may be combined with any of the structures described in the other embodiments as needed. (Embodiment 4)

[0103] In this embodiment, an embodiment of a light-emitting device in which the light-emitting element described in Embodiment 1 is combined with a color layer (a color filter or the like) is described. In this embodiment, the structure of a pixel portion of the light-emitting device is described with reference to Fig. 5 described.

[0104] In Fig. 5, a plurality of FETs (transistors) 502 are formed over a substrate 501. Each of the FETs 502 is electrically connected to a light-emitting element (507R, 507G, 507B, or 507Y). Specifically, each of the FETs 502 is electrically connected to a first electrode 503, which is a pixel electrode of the light-emitting element. A partition wall 504 is provided to cover end portions of the adjacent first electrodes 503.

[0105] The first electrode 503 in this embodiment functions as a reflective electrode. An EL layer 505 is formed over the first electrode 503, and a second electrode 510 is formed over the EL layer 505. The EL layer 505 includes a plurality of light-emitting layers, each emitting monochromatic light. The second electrode 510 functions as a semi-transparent and semi-reflective electrode.

[0106] The light-emitting elements (507R, 507G, 507B, and 507Y) emit light of different colors. Specifically, the light-emitting element 507R is optically adjusted to emit red light, and in a region indicated by 506R, red light is emitted through a color layer 508R in the direction indicated by an arrow. The light-emitting element 507G is optically adjusted to emit green light, and in a region indicated by 506G, green light is emitted through a color layer 508G in the direction indicated by an arrow. The light-emitting element 507B is optically adjusted to emit blue light, and in a region indicated by 506B, blue light is emitted through a color layer 508B in the direction indicated by an arrow.The light-emitting element 507Y is optically adjusted to emit yellow light, and in a region indicated by 506Y, yellow light is emitted through a color layer 508Y in the direction indicated by an arrow.

[0107] As in Fig. As shown in Figure 5, each of the color layers (508R, 508G, 508B, and 508Y) is provided on a transparent sealing substrate 511 provided over the substrate 501 over which the light-emitting elements (507R, 507G, 507B, and 507Y) are formed. Note that the color layers (508R, 508G, 508B, and 508Y) are provided at positions overlapping the corresponding light-emitting elements (507R, 507G, 507B, and 507Y) having different emission colors.

[0108] A black layer (black matrix) 509 is provided to overlap end portions of the adjacent color layers (508R, 508G, 508B, and 508Y). Note that the color layers (508R, 508G, 508B, and 508Y) as well as the black layer 509 may be covered with a covering layer formed using a transparent material.

[0109] The light-emitting device described above has a structure in which light is extracted from the sealing substrate 511 side (a top emission structure), but it may also have a structure in which light is extracted from the side of the substrate 501 where the FETs are formed (a bottom emission structure). Note that in the light-emitting device having a top emission structure described in this embodiment, a light-blocking substrate or a light-transmitting substrate can be used as the substrate 501, whereas in a light-emitting device having a bottom emission structure, a light-transmitting substrate must be used as the substrate 501.

[0110] For example, in this specification and the like, a transistor or a light-emitting element can be formed using any of various substrates. The type of substrate is not limited to a specific type. For example, a semiconductor substrate (e.g., a single-crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate including a stainless steel foil, a tungsten substrate, a substrate including a tungsten foil, a flexible substrate, an attachment film, paper containing a fiber material, a base material film, or the like can be used as the substrate. Examples of a glass substrate include a barium borosilicate glass substrate, an aluminum borosilicate glass substrate, and a soda-lime glass substrate.Examples of the flexible substrate, the fixing film, the base material film, and the like include plastics such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), and polytetrafluoroethylene (PTFE); a synthetic resin such as acrylic; films formed of polypropylene, polyester, polyvinyl fluoride, and polyvinyl chloride; films formed of polyamide, polyimide, aramid, and epoxy; an inorganic film formed by evaporation; and paper. Specifically, when a transistor is manufactured using a semiconductor substrate, a single-crystal substrate, an SOI substrate, or the like, a transistor with small variations in characteristics, size, shape, etc., with a high power supply capability, and a small size can be manufactured.A circuit using such a transistor has lower power consumption or higher integration.

[0111] Alternatively, a flexible substrate may be used as the substrate, and the transistor or light-emitting element may be provided directly above the flexible substrate. As a further alternative, a separation layer may be provided between a substrate and the transistor or the like. The separation layer may be used when part or all of the semiconductor device formed above the separation layer is separated from the substrate and transferred to another substrate. In such a case, the transistor or the like may also be transferred to a substrate with low heat resistance or to a flexible substrate.For the separation layer described above, for example, a layer assembly comprising inorganic films, namely a tungsten film and a silicon oxide film, or an organic resin film of polyimide or the like formed over a substrate can be used.

[0112] In other words, after the transistor or light-emitting element is formed using one substrate, the transistor or light-emitting element can be transferred to another substrate. Examples of a substrate onto which the transistor or light-emitting element is transferred include, in addition to the above-described substrates over which a transistor or the like can be formed, a paper substrate, a cellophane substrate, an aramid film substrate, a polyimide film substrate, a stone substrate, a wood substrate, a fabric substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupro, viscose, or regenerated polyester), or the like), a leather substrate, and a rubber substrate.When such a substrate is used, a transistor or the like having excellent characteristics or low power consumption can be formed, a device having high durability and high heat resistance can be provided, or a reduction in weight or thickness can be achieved.

[0113] It should be noted that the structure described in this embodiment may be combined with any of the structures described in the other embodiments as needed. (Embodiment 5)

[0114] In this embodiment, a light-emitting device including a light-emitting element using a dibenzo[f,h]quinoxaline derivative for an EL layer is described.

[0115] The light-emitting device can be either a passive matrix light-emitting device or an active matrix light-emitting device. Note that any of the light-emitting elements described in the other embodiments can be applied to a light-emitting device described in this embodiment.

[0116] In this embodiment, an active matrix light-emitting device is manufactured using Fig. 6A and Fig. 6B.

[0117] Fig. Fig. 6A is a plan view illustrating the light-emitting device, and Fig. Figure 6B is a cross-sectional view taken along the dot-dash line AA' of Fig. 6A. The active matrix light-emitting device of this embodiment includes a pixel portion 602 provided above an element substrate 601, a driving circuit portion (a source line driving circuit) 603, and driving circuit portions (gate line driving circuits) 604a and 604b. The pixel portion 602, the driving circuit portion 603, and the driving circuit portions 604a and 604b are sealed with a sealant 605 between the element substrate 601 and a sealing substrate 606.

[0118] Furthermore, a lead wire 607 for connecting an external input terminal is provided above the element substrate 601, through which a signal (e.g., a video signal, a clock signal, a start signal, a reset signal, or the like) or a potential is transmitted from the outside to the drive circuit section 603 and the drive circuit sections 604a and 604b. Here, an example will be described in which a flexible printed circuit (FPC) 608 is provided as the external input terminal. Although only the FPC is illustrated here, the FPC may be provided with a printed wiring board (PWB). The light-emitting device in this specification includes within its category not only the light-emitting device itself but also the light-emitting device provided with an FPC or a PWB.

[0119] Next, a cross-sectional structure is created based on Fig. 6B. The driver circuit portions and the pixel portion are formed over the element substrate 601; here, the driver circuit portion 603, which is the source line driver circuit, and the pixel portion 602 are shown.

[0120] For example, an FET 609 and an FET 610 are combined in the driver circuit section 603. Note that the driver circuit section 603 may be formed with a circuit including transistors of the same conductivity type (either n-channel transistors or p-channel transistors) or with a CMOS circuit including an n-channel transistor and a p-channel transistor. In this embodiment, a driver-integrated type is shown in which a driver circuit is formed over a substrate; however, the driver circuit may also be formed outside the substrate.

[0121] The pixel section 602 includes a plurality of pixels, each including a switching FET 611, a current control FET 612, and a first electrode (anode) 613 electrically connected to a lead (a source electrode or a drain electrode) of the current control FET 612. In this embodiment, the pixel section 602 includes two FETs, namely the switching FET 611 and the current control FET 612; however, an embodiment of the present invention is not limited thereto. The pixel section 602 may include, for example, three or more FETs in combination with a capacitor.

[0122] For example, a staggered transistor or an inverted staggered transistor can be used for FETs 609, 610, 611, and 612. Examples of semiconductor materials that can be used for FETs 609, 610, 611, and 612 include Group 13 semiconductors (e.g., gallium), Group 14 semiconductors (e.g., silicon), compound semiconductors, oxide semiconductors, and organic semiconductors. Furthermore, there is no particular limitation on the crystallinity of the semiconductor material, and, for example, an amorphous semiconductor film or a crystalline semiconductor film can be used. Preferably, an oxide semiconductor is used for FETs 609, 610, 611, and 612. Examples of the oxide semiconductor include an In-Ga oxide and an In-M-Zn oxide (M represents Al, Ga, Y, Zr, La, Ce or Nd).For example, an oxide semiconductor material having an energy gap of 2 eV or larger, preferably 2.5 eV or larger, more preferably 3 eV or larger, is used for the FETs 609, 610, 611 and 612, so that the off-state current of the transistors can be reduced.

[0123] An insulator 614 is formed to cover an end portion of the first electrode 613. In this embodiment, the insulator 614 is formed using a positive photosensitive acrylic resin. The first electrode 613 is used as an anode in this embodiment.

[0124] The insulator 614 preferably has a curved surface with a curve at its upper end portion or lower end portion. This allows for advantageous coverage with a film formed over the insulator 614. For example, the insulator 614 can be formed using either a negative photosensitive resin or a positive photosensitive resin. The material for the insulator 614 is not limited to an organic compound, and an inorganic compound such as silicon oxide, silicon oxynitride, or silicon nitride can also be used.

[0125] An EL layer 615 and a second electrode (cathode) 616 are disposed above the first electrode (anode) 613. At least one light-emitting layer is provided in the EL layer 615. Furthermore, in addition to the light-emitting layer, a hole-injection layer, a hole-transport layer, an electron-transport layer, an electron-injection layer, a charge-generation layer, and the like may be provided in the EL layer 615 as needed.

[0126] A light-emitting element 617 is formed from a multilayer structure of the first electrode (anode) 613, the EL layer 615, and the second electrode (cathode) 616. The materials described in Embodiment 2 can be used for the first electrode (anode) 613, the EL layer 615, and the second electrode (cathode) 616. Although not shown here, the second electrode (cathode) 616 is electrically connected to the FPC 608, which is an external input terminal.

[0127] Although the cross-sectional view in Fig. 6B illustrates only one light-emitting element 617, a plurality of light-emitting elements are arranged in a matrix in the pixel portion 602. Light-emitting elements that emit light of three kinds of colors (R, G, and B) are selectively formed in the pixel portion 602, whereby a light-emitting device suitable for full-color display can be manufactured. In addition to the light-emitting elements that emit light of three kinds of colors (R, G, and B), for example, light-emitting elements that emit light of white (W), yellow (Y), magenta (M), cyan (C), and the like can be formed. For example, the light-emitting elements that emit light of a plurality of kinds of colors are used in combination with the light-emitting elements that emit light of three kinds of colors (R, G, and B), thereby achieving effects such as color shifting.An improvement in color purity and a reduction in power consumption can be achieved. Alternatively, a light-emitting device suitable for full-color display can be produced by combining it with color filters. Furthermore, the light-emitting device can exhibit improved emission efficiency and reduced power consumption by combining it with quantum dots.

[0128] The sealing substrate 606 is attached to the element substrate 601 with the sealant 605 such that the light-emitting element 617 is provided in a space 618 enclosed by the element substrate 601, the sealing substrate 606, and the sealant 605. The space 618 may be filled with an inert gas (such as nitrogen or argon) or with the sealant 605.

[0129] For the sealant 605, an epoxy-based resin or a glass frit is preferably used. It is preferable that such a material permits as little moisture or oxygen permeation as possible. A glass substrate, a quartz substrate, or a plastic substrate formed of fiber-reinforced plastics (FRP), polyvinyl fluoride (PVF), polyester, acrylic, or the like can be used as the element substrate 601 and the seal substrate 606. In the case where a glass frit is used as the sealant, the element substrate 601 and the seal substrate 606 are preferably glass substrates for high adhesion.

[0130] In the manner described above, an active matrix light-emitting device can be obtained.

[0131] It should be noted that the structure described in this embodiment may be combined with any of the structures described in the other embodiments as needed. (Embodiment 6)

[0132] In this embodiment, various examples of an electronic device manufactured using a light-emitting device of one embodiment of the present invention will be described with reference to Fig. 7A to Fig. 7D described.

[0133] Examples of an electronic device to which a light-emitting device is applied include television sets (also referred to as televisions or television receivers), monitors for computers and the like, cameras such as digital cameras and digital video cameras, digital photo frames, mobile phones (also referred to as cellular phones or portable telephone devices), portable game consoles, portable information terminals, audio playback devices, and large gaming machines such as pinball machines. Specific examples of these electronic devices are described in Fig. 7A to Fig. 7D.

[0134] Fig. 7A illustrates an example of a television set. In a television set 7100, a display section 7103 is installed in a housing 7101. The display section 7103 can display images, and it can be a touch screen (an input / output device) that includes a touch sensor (an input device). Note that the light-emitting device, which is an embodiment of the present invention, can be used for the display section 7103. In addition, here, the housing 7101 is supported by a stand 7105.

[0135] The television set 7100 can be operated using a power switch on the housing 7101 or using a separate remote control 7110. Using control buttons 7109 on the remote control 7110, the television channels and volume can be adjusted, and images displayed on the display section 7103 can be controlled. Furthermore, the remote control 7110 can be provided with a display section 7107 for displaying the information output by the remote control 7110.

[0136] Note that the television 7100 is equipped with a receiver, a modem, and the like. Using the receiver, general television broadcasting can be received. Furthermore, when the television is connected to a communication network via a modem, either wirelessly or wirelessly, unidirectional (from a transmitter to a receiver) or bidirectional (between a transmitter and a receiver, or between receivers) information communication can be performed.

[0137] Fig. 7B illustrates a computer including a main body 7201, a casing 7202, a display section 7203, a keyboard 7204, an external connection port 7205, a pointing device 7206, and the like. Note that this computer can be manufactured by using the light-emitting device, which is an embodiment of the present invention, for the display section 7203. The display section 7203 may be a touchscreen (an input / output device) that includes a touch sensor (an input device).

[0138] Fig. 7C illustrates a smartwatch including a case 7302, a display panel 7304, operation buttons 7311 and 7312, a connection terminal 7313, a band 7321, a clasp 7322, and the like.

[0139] The display panel 7304, mounted in the housing 7302 serving as a bezel, has a non-rectangular display area. The display panel 7304 can display an icon 7305 that displays the time, another icon 7306, and the like. The display panel 7304 can be a touchscreen (an input / output device) that includes a touch sensor (an input device).

[0140] The smartwatch that Fig. 7C may have various functions such as a function of displaying various information (e.g., a still image, a moving image, and a text image) on a display portion, a touch screen function, a function of displaying a calendar, a date, a time, and the like, a function of controlling processing by means of various software (programs), a wireless communication function, a function of connecting to various computer networks by means of a wireless communication function, a function of transmitting and receiving various data by means of a wireless communication function, and a function of reading a program or data stored in a storage medium and displaying the program or data on a display portion.

[0141] The housing 7302 may include a speaker, a sensor (a sensor with a function for measuring force, displacement, position, speed, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays), a microphone, and the like. Note that the smartwatch can be manufactured by using the light-emitting device for the display panel 7304.

[0142] Fig. 7D illustrates an example of a mobile phone (e.g., a smartphone). A mobile phone 7400 includes a housing 7401 provided with a display portion 7402, a microphone 7406, a speaker 7405, a camera 7407, an external connection terminal 7404, an operation button 7403, and the like. In the case where a light-emitting device is manufactured by forming the light-emitting element of one embodiment of the present invention over a flexible substrate, the light-emitting device for the display portion 7402 may have a curved surface as shown in Fig. 7D.

[0143] When the display section 7402 of the mobile phone 7400, which is in Fig. 7D is touched with a finger or the like, information can be input into the mobile phone. Furthermore, operations such as making a call and composing an email can be performed by touching the display section 7402 with a finger or the like.

[0144] There are essentially three screen modes for the display section 7402. The first mode is a display mode, which primarily displays images. The second mode is an input mode, which primarily inputs information such as characters. The third mode is a display and input mode, which combines two modes: a display mode and an input mode.

[0145] For example, in the case of making a call or composing an email, a text input mode that primarily inputs characters is selected for the display section 7402 so that characters displayed on the screen can be input. In this case, it is preferable that a keyboard or number keys be displayed on almost the entire screen of the display section 7402.

[0146] When a detection device such as a gyroscope or an acceleration sensor is provided in the mobile phone 7400, the display on the screen of the display section 7402 can be automatically switched by determining the orientation of the mobile phone 7400 (whether the mobile phone is positioned horizontally or vertically for a landscape or portrait orientation).

[0147] The screen modes are switched by touching the display section 7402 or by operating the operation knob 7403 of the body 7401. The screen modes can also be switched depending on the type of images displayed on the display section 7402. For example, if a signal of an image displayed on the display section is a moving image data signal, the screen mode is switched to the display mode. If the signal is a text data signal, the screen mode is switched to the input mode.

[0148] Moreover, in the input mode, when a signal detected by an optical sensor in the display section 7402 is detected and the input by touching the display section 7402 is not performed within a certain period of time, the screen mode can be controlled to switch from the input mode to the display mode.

[0149] The display section 7402 can serve as an image sensor. For example, an image of a palm print, a fingerprint, or the like can be captured by touching the display section 7402 with the palm or finger, thereby performing personal authentication. Furthermore, if a backlight or a scanning light source that emits near-infrared light is provided in the display section, an image of a finger vein, a palm vein, or the like can be captured.

[0150] Furthermore, the light-emitting device can also be used for a mobile phone having a structure shown in Fig. 7D' Fig. 1 or Fig. 7D' Fig. 2, which is another structure of the mobile phone (e.g. smartphone).

[0151] In the case of the structure described in Fig. 7D' Fig. 1 or Fig. 7D' Fig. 2, text data, image data, or the like can be displayed on second screens 7502(1) and 7502(2) of casings 7500(1) and 7500(2), as well as on first screens 7501(1) and 7501(2). Such a structure allows a user to easily view text data, image data, or the like displayed on the second screens 7502(1) and 7502(2) while the mobile phone is placed in a user's breast pocket.

[0152] Fig. 8A to Fig. 8C illustrate a foldable, portable information terminal 9310. Fig. 8A illustrates the portable information terminal 9310 unfolded. Fig. 8B illustrates the portable information terminal 9310 being opened or closed. Fig. 8C illustrates the portable information terminal 9310 in the folded state. The portable information terminal 9310 is highly portable when folded. When the portable information terminal 9310 is unfolded, a seamless, large display area is highly searchable.

[0153] A display panel 9311 is supported by three housings 9315 connected to each other by hinges 9313. The display panel 9311 may be a touchscreen (an input / output device) incorporating a touch sensor (an input device). The portable information terminal 9310 can be reversibly changed in shape from an unfolded state to a folded state by bending the display panel 9311 using the hinges 9313 at a junction between two housings 9315. The light-emitting device of one embodiment of the present invention can be used for the display panel 9311. A display region in the display panel 9311 includes a display region positioned on a side surface of the folded portable information terminal 9310.Information icons, frequently used applications, program shortcuts, and the like can be displayed on this display area, and confirmation of information and launching of applications can be easily performed.

[0154] As described above, electronic devices can be obtained using the light-emitting device of one embodiment of the present invention. Note that the light-emitting device can be used for electronic devices in various fields, without being limited to the electronic devices described in this embodiment.

[0155] It should be noted that the structure described in this embodiment may be combined with any of the structures described in the other embodiments as needed. (Embodiment 7)

[0156] In this embodiment, examples of a lighting device to which a light-emitting device of one embodiment of the present invention is applied will be explained with reference to Fig. 9 described.

[0157] Fig. 9 illustrates an example in which the light-emitting device is used as an indoor lighting device 8001. Since the area of ​​the light-emitting device can be increased, a lighting device having a large area can be formed. In addition, by using a housing with a curved surface, a lighting device 8002 including the housing, a cover, or a holder, and in which a light-emitting portion has a curved surface can be obtained. A light-emitting element included in the light-emitting device described in this embodiment is in the form of a thin film, which makes it possible to design the housing more freely. Consequently, the lighting device can be artistically designed in various ways. Furthermore, a wall of the room can be provided with a large lighting device 8003.

[0158] Furthermore, when the light-emitting device is used for a table, by using it as the surface of the table, a lighting device 8004 having a function as a table can be obtained. When the light-emitting device is used as part of another piece of furniture, a lighting device having a function as the piece of furniture in question can be obtained.

[0159] In this way, various lighting devices to which the light-emitting device is applied can be obtained. It should be noted that such lighting devices are also embodiments of the present invention.

[0160] It should be noted that the structure described in this embodiment may be combined with any of the structures described in the other embodiments as needed. [Example 1]<<Synthesebeispiel 1> >

[0161] In this example, a synthesis method of 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2PCCzPDBq, which is represented by structural formula (100)) is described as a synthesis method of one embodiment of the present invention. The structure of 2PCCzPDBq is shown below. <Synthese von 2PCCzPDBq>

[0162] First, 1.0 g (2.8 mmol) of 2-(4-chlorophenyl)dibenzo[f,h]quinoxaline, 1.1 g (2.8 mmol) of 3-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole, 0.54 g (5.6 mmol) of sodium tert-butoxide, and 23 mg (0.10 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (abbreviation: S-Phos) were placed in a 200 mL three-necked flask and mixed, and the air in the flask was replaced with nitrogen. 14 mL of mesitylene was added to this mixture, and the resulting mixture was degassed by stirring while reducing the pressure in the flask.

[0163] Subsequently, 16 mg (0.028 mmol) of bis(dibenzylideneacetone)palladium(0) (abbreviation: Pd(dba)2) was added to the mixture. This mixture was stirred at 150 °C for 5 hours under a nitrogen stream, causing a solid to precipitate. The precipitated solid was collected by suction filtration. The collected solid was dissolved in approximately 400 mL of hot toluene, and this solution was subjected to suction filtration through a layered arrangement of Celite and alumina. The obtained filtrate was concentrated to obtain a solid. The solid was recrystallized with toluene to obtain 1.6 g of a yellow powder, which was the target substance, in an 80% yield.

[0164] Using a train sublimation process, 1.4 g of the resulting yellow powdery solid, which was the target substance, was purified. The sublimation purification was carried out at 380 °C under a pressure of 3.8 Pa with an argon gas flow rate of 10 ml / min. After the sublimation purification, 1.1 g of a yellow, glassy solid of 2PCCzPDBq was obtained with a collection rate of 79%. The synthesis scheme for this step is shown in Scheme (a-1) below.

[0165] Analysis results obtained by nuclear magnetic resonance spectroscopy ( 1 H-NMR) of the yellow powdery solid obtained in the above step are described below. 1 H-NMR diagrams are in Fig. 10A and Fig. 10B shown. Fig. Figure 10B is a graph in which the range from 7.0 (ppm) to 10 (ppm) is plotted on the horizontal axis (δ) in Fig. 10A. These results indicate that 2PCCzPDBq (represented by structural formula (100)) was obtained in the above step.

[0166] δ = 7.32 (t, J = 5.7 Hz, 1H), 7.37 (t, J = 8.0 Hz, 1H), 7.43-7.53 (m, 5H), 7.58-7.66 (m, 6H), 7.72-7.89 (m, 8H), 8.25 (d, J = 7.4Hz, 1H), 8.30 (d, J = 8.1 Hz, 1H), 8.44 (d, J = 7.5 Hz, 1H), 8.50 (d, J = 5.4 Hz, 2H), 8.64-8.67 (m, 3H), 9.25 (d, J = 8.0 Hz, 1H), 9.37 (d, J = 6.3 Hz, 1H), 9.47 (s, 1H).

[0167] In addition, Fig. 11 the absorption spectrum and the emission spectrum of 2PCCzPDBq in a 2PCCzPDBq toluene solution, and Fig. Figure 12 shows the absorption spectrum and emission spectrum of 2PCCzPDBq in a 2PCCzPDBq thin film. The spectra were measured using a UV / VIS (UV-visible) spectrophotometer (V550, manufactured by JASCO Corporation). The spectra of 2PCCzPDBq in the 2PCCzPDBq toluene solution were measured using a quartz cell. The spectra of 2PCCzPDBq in the 2PCCzPDBq thin film were measured using a sample prepared by evaporatively depositing 2PCCzPDBq on a quartz substrate.It should be noted that in the case of the absorption spectrum of 2PCCzPDBq in the 2PCCzPDBq-toluene solution, the absorption spectrum obtained by subtracting the absorption spectra of the quartz cell and toluene from the measured spectrum is shown, and that in the case of the absorption spectrum of 2PCCzPDBq in the 2PCCzPDBq thin film, the absorption spectrum obtained by subtracting the absorption spectrum of the quartz substrate from the measured spectrum is shown.

[0168] In the case of 2PCCzPDBq in the 2PCCzPDBq-toluene solution, as described in Fig. 11, the absorption peaks were observed at approximately 305 nm and 385 nm, and the emission wavelength peak was observed at 450 nm (excitation wavelength: 305 nm). In the case of 2PCCzPDBq in the 2PCCzPDBq thin film, as shown in Fig. 12, the absorption peaks were observed at approximately 209 nm, 258 nm, 307 nm, 336 nm and 396 nm, and the emission wavelength peak was observed at 502 nm (excitation wavelength: 396 nm). [Example 2]<<Synthesebeispiel 2> >

[0169] This example describes a synthetic method for 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq, which is represented by structural formula (101)). The structure of 2mPCCzPDBq is shown below. <Synthese von 2mPCCzPDBq>

[0170] First, 1.7 g (5.0 mmol) of 2-(3-chlorophenyl)dibenzo[f,h]quinoxaline, 2.0 g (5.0 mmol) of 3-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole, 0.96 g (10 mmol) of sodium tert-butoxide, and 41 mg (0.10 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (abbreviation: S-Phos) were placed in a 200 mL three-necked flask and mixed, and the air in the flask was replaced with nitrogen. 25 mL of mesitylene was added to this mixture, and the resulting mixture was degassed by stirring while reducing the pressure in the flask.

[0171] Subsequently, 29 mg (0.050 mmol) of bis(dibenzylideneacetone)palladium(0) (abbreviation: Pd(dba)2) was added to the mixture. This mixture was stirred at 150 °C for 5 hours under a nitrogen stream, causing a solid to precipitate. The precipitated solid was collected by suction filtration. The collected solid was dissolved in approximately 400 mL of hot toluene, and this solution was subjected to suction filtration through a layered arrangement of Celite and alumina. The obtained filtrate was concentrated to obtain a solid. The solid was recrystallized with toluene to obtain 2.8 g of a yellow powder, which was the target substance, in a yield of 79%.

[0172] Using a train sublimation process, 2.2 g of the resulting yellow powdery solid, which was the target substance, was purified. The sublimation purification was carried out at 360 °C under a pressure of 2.5 Pa with an argon gas flow rate of 10 ml / min. After the sublimation purification, 1.2 g of a yellow, glassy solid of 2mPCCzPDBq was obtained with a collection rate of 55%. The synthesis scheme for this step is shown in Scheme (b-1) below.

[0173] Analysis results obtained by nuclear magnetic resonance spectroscopy ( 1 H-NMR) of the yellow powdery solid obtained in the above step are described below. 1 H-NMR diagrams are in Fig. 13A and Fig. 13B shown. Fig. Figure 13B is a graph in which the range from 7.0 (ppm) to 10 (ppm) is plotted on the horizontal axis (δ) in Fig. 13A. These results indicate that 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq, which is represented by structural formula (101)) was obtained in the above step.

[0174] 1 H-NMR (CDCl3, 500 MHz): δ (ppm) = 7.31-7.54 (m, 7H), 7.58-7.67 (m, 6H), 7.73-7.90 (m, 8H), 8.25 (d, J = 8.0 Hz, 1H), 8.30 (d, J = 8.1 Hz, 1H), 8.45 (d, J = 6.3 Hz, 1H), 8.49 (d, J = 3.7 Hz, 2H), 8.65-8.68 (m, 3H), 9.25 (d, J = 2.0 Hz, 1H), 9.37 (d, J = 6.9 Hz, 1H), 9.48 (s, 1H).

[0175] In addition, Fig. 14 the absorption spectrum and the emission spectrum of 2mPCCzPDBq in a 2mPCCzPDBq toluene solution, and Fig. Figure 15 shows the absorption spectrum and emission spectrum of 2mPCCzPDBq in a 2mPCCzPDBq thin film. The spectra were measured using a UV / VIS spectrophotometer (V550, manufactured by JASCO Corporation). The spectra of 2mPCCzPDBq in the 2mPCCzPDBq toluene solution were measured by placing the 2mPCCzPDBq toluene solution in a quartz cell. The spectra of 2mPCCzPDBq in the 2mPCCzPDBq thin film were measured using a sample prepared by evaporatively depositing 2mPCCzPDBq on a quartz substrate.It should be noted that in the case of the absorption spectrum of 2mPCCzPDBq in the 2mPCCzPDBq-toluene solution, the absorption spectrum obtained by subtracting the absorption spectra of the quartz cell and toluene from the measured spectrum is shown, and that in the case of the absorption spectrum of 2mPCCzPDBq in the 2mPCCzPDBq thin film, the absorption spectrum obtained by subtracting the absorption spectrum of the quartz substrate from the measured spectrum is shown.

[0176] In the case of 2mPCCzPDBq in the 2mPCCzPDBq-toluene solution, as described in Fig. 14, the absorption peaks were observed at approximately 305 nm and 374 nm, and the emission wavelength peak was observed at 480 nm (excitation wavelength: 305 nm). In the case of 2mPCCzPDBq in the 2mPCCzPDBq thin film, as shown in Fig. 15, the absorption peaks were observed at approximately 208 nm, 257 nm, 308 nm, 361 nm and 379 nm, and the emission wavelength peak was observed at 515 nm (excitation wavelength: 380 nm). [Example 3]<<Synthesebeispiel 3> >

[0177] This example describes a synthetic method for 2-{4-[2-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2PCCzPDBq-02, represented by structural formula (102)). The structure of 2PCCzPDBq-02 is shown below. <Synthese von 2PCCzPDBq-02>

[0178] First, 1.4 g (4.2 mmol) of 2-(4-chlorophenyl)dibenzo[f,h]quinoxaline, 1.7 g (4.2 mmol) of 2-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole, 0.81 g (8.4 mmol) of sodium tert-butoxide, and 34 mg (0.10 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (abbreviation: S-Phos) were placed in a 200 mL three-necked flask and mixed, and the air in the flask was replaced with nitrogen. 21 mL of mesitylene was added to this mixture, and the resulting mixture was degassed by stirring while reducing the pressure in the flask.

[0179] Subsequently, 24 mg (0.042 mmol) of bis(dibenzylideneacetone)palladium(0) (abbreviation: Pd(dba)2) was added to the mixture. This mixture was stirred at 150 °C for 5 hours under a nitrogen stream, causing a solid to precipitate. The precipitated solid was collected by suction filtration. The collected solid was dissolved in approximately 400 mL of hot toluene, and this solution was subjected to suction filtration through a layered arrangement of Celite and alumina. The obtained filtrate was concentrated to obtain a solid. The solid was recrystallized with toluene to obtain 2.5 g of a yellow powder, which was the target substance, in an 84% yield.

[0180] Using a train sublimation process, 2.0 g of the resulting yellow powdery solid, which was the target substance, was purified. The sublimation purification was carried out at 390 °C under a pressure of 3.7 Pa with an argon gas flow rate of 10 ml / min. After the sublimation purification, 1.7 g of a yellow, glassy solid of 2PCCzPDBq-02 was obtained with a collection rate of 85%. The synthesis scheme for this step is shown in Scheme (c-1) below.

[0181] Analysis results obtained by nuclear magnetic resonance spectroscopy ( 1 H-NMR) of the yellow powdery solid obtained in the above step are described below. 1 H-NMR diagrams are in Fig. 16A and Fig. 16B shown. Fig. Figure 16B is a graph in which the range from 7.0 (ppm) to 10 (ppm) is plotted on the horizontal axis (δ) in Fig. 16A. These results indicate that 2-{4-[2-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2PCCzPDBq-02, which is represented by structural formula (102)) was obtained in the above step.

[0182] δ= 7.25-7.48 (m, 7H), 7.71-7.75 (m, 2H), 7.71-7.75 (m, 5H), 7.91 (d, J = 8.6 Hz, 2H), 8.21 (d, J = 7.4 Hz, 1H), 8.26 (d, J = 8.0 Hz, 2H), 8.42 (sd, J = 1.7 Hz, 2H), 8.63-8.69 (m, 4H), 9.27 (d, J = 8.0 Hz, 1H), 9.46 (d, J = 6.3 Hz, 1H), 9.51 (s, 1H).

[0183] In addition, Fig. 17 the absorption spectrum and the emission spectrum of 2PCCzPDBq-02 in a 2PCCzPDBq-02 toluene solution, and Fig. Figure 18 shows the absorption spectrum and emission spectrum of 2PCCzPDBq-02 in a 2PCCzPDBq-02 thin film. The spectra were measured using a UV / VIS spectrophotometer (V550, manufactured by JASCO Corporation). The spectra of 2PCCzPDBq-02 in the 2PCCzPDBq-02 toluene solution were measured by placing the 2PCCzPDBq-02 toluene solution in a quartz cell. The spectra of 2PCCzPDBq-02 in the 2PCCzPDBq-02 thin film were measured using a sample prepared by evaporatively depositing 2PCCzPDBq-02 on a quartz substrate.It should be noted that in the case of the absorption spectrum of 2PCCzPDBq-02 in the 2PCCzPDBq-02 toluene solution, the absorption spectrum obtained by subtracting the absorption spectra of the quartz cell and toluene from the measured spectrum is shown, and that in the case of the absorption spectrum of 2PCCzPDBq-02 in the 2PCCzPDBq-02 thin film, the absorption spectrum obtained by subtracting the absorption spectrum of the quartz substrate from the measured spectrum is shown.

[0184] In the case of 2PCCzPDBq-02 in the 2PCCzPDBq-02 toluene solution, as in Fig. 17, the absorption peaks were observed at approximately 323 nm and 381 nm, and the emission wavelength peak was observed at 421 nm (excitation wavelength: 320 nm). In the case of 2PCCzPDBq-02 in the 2PCCzPDBq-02 thin film, as shown in Fig. 18, the absorption peaks were observed at approximately 209 nm, 257 nm, 311 nm, 326 nm, 351 nm and 389 nm, and the emission wavelength peak was observed at 473 nm (excitation wavelength: 396 nm). [Example 4]<<Synthesebeispiel 4> >

[0185] This example describes a synthetic method for 2-{3-[2-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq-02, represented by structural formula (103)). The structure of 2mPCCzPDBq-02 is shown below. <Synthese von 2mPCCzPDBq-02>

[0186] First, 1.7 g (5.0 mmol) of 2-(3-chlorophenyl)dibenzo[f,h]quinoxaline, 2.0 g (5.0 mmol) of 2-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole, 0.96 g (10 mmol) of sodium tert-butoxide, and 41 mg (0.10 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (abbreviation: S-Phos) were placed in a 200 mL three-necked flask and mixed, and the air in the flask was replaced with nitrogen. 25 mL of mesitylene was added to this mixture, and the resulting mixture was degassed by stirring while reducing the pressure in the flask.

[0187] Subsequently, 29 mg (0.050 mmol) of bis(dibenzylideneacetone)palladium(0) (abbreviation: Pd(dba)2) was added to the mixture. This mixture was stirred at 150 °C for 4 hours under a nitrogen stream, causing a solid to precipitate. The precipitated solid was collected by suction filtration. The collected solid was dissolved in approximately 400 mL of hot toluene, and this solution was subjected to suction filtration through a layered assembly of Celite, alumina, and Florisil. The obtained filtrate was concentrated to obtain a solid. The solid was recrystallized with toluene to obtain 3.1 g of a white powder, which was the target substance, in an 87% yield.

[0188] Using a train sublimation process, 3.0 g of the resulting white powdery solid, which was the target substance, was purified. The sublimation purification was carried out at 360 °C under a pressure of 10 Pa with an argon gas flow rate of 5.0 ml / min. After the sublimation purification, 2.0 g of a yellow, glassy solid of 2mPCCzPDBq-02 was obtained with a collection rate of 65%. The synthesis scheme of this step is shown in Scheme (d-1) below.

[0189] Analysis results obtained by nuclear magnetic resonance spectroscopy ( 1 H-NMR) of the white powdery solid obtained in the above step are described below. 1 H-NMR diagrams are in Fig. 19A and Fig. 19B shown. Fig. Figure 19B is a graph in which the range from 7.0 (ppm) to 10 (ppm) is plotted on the horizontal axis (δ) in Fig. 19A. These results indicate that 2mPCCzPDBq-02 (represented by structural formula (103)) was obtained in the above step.

[0190] 1 H-NMR (DMSO-d 6 , 500 MHz): δ (ppm) = 7.17 (t, J1 = 7.5 Hz, 1H), 7.31-7.39 (m, 4H), 7.47-7.52 (m, 2H), 7.56-7.57 (m, 3H), 7.63-7.66 (m, 3H), 7.75-7.92 (m, 7H), 7.98 (t, J1 = 2.5 Hz, 1H), 8.19 (d, J1 = 7.5 Hz, 1H), 8.30 (d, J1 = 7.5 Hz, 1H), 8.37 (d, J1 = 8.0 Hz, 1H), 8.54 (sd, J1 = 1.5 Hz, 1H), 8.62 (d, J1 = 8.0 Hz, 1H), 8.79-8.82 (m, 3H), 9.19 (d, J1 = 8.0 Hz, 1H), 9.25 (d, J1 = 9.0 Hz, 1H), 9.75 (s, 1H).

[0191] In addition, Fig. 20 the absorption spectrum and the emission spectrum of 2mPCCzPDBq-02 in a 2mPCCzPDBq-02 toluene solution, and Fig. Figure 21 shows the absorption spectrum and emission spectrum of 2mPCCzPDBq-02 in a 2mPCCzPDBq-02 thin film. The spectra were measured using a UV / VIS spectrophotometer (V550, manufactured by JASCO Corporation). The spectra of 2mPCCzPDBq-02 in the 2mPCCzPDBq-02 toluene solution were measured by placing the 2mPCCzPDBq-02 toluene solution in a quartz cell. The spectra of 2mPCCzPDBq-02 in the 2mPCCzPDBq-02 thin film were measured using a sample prepared by evaporatively depositing 2mPCCzPDBq-02 on a quartz substrate.It should be noted that in the case of the absorption spectrum of 2mPCCzPDBq-02 in the 2mPCCzPDBq-02 toluene solution, the absorption spectrum obtained by subtracting the absorption spectra of the quartz cell and toluene from the measured spectrum is shown, and that in the case of the absorption spectrum of 2mPCCzPDBq-02 in the 2mPCCzPDBq-02 thin film, the absorption spectrum obtained by subtracting the absorption spectrum of the quartz substrate from the measured spectrum is shown.

[0192] In the case of 2mPCCzPDBq-02 in the 2mPCCzPDBq-02 toluene solution, as described in Fig. 20, the absorption peaks were observed at approximately 281 nm, 305 nm, 319 nm, and 374 nm, and the emission wavelength peaks were observed at 389 nm and 410 nm. In the case of 2mPCCzPDBq-02 in the 2mPCCzPDBq-02 thin film, as shown in Fig. 21, the absorption peaks were observed at approximately 209 nm, 257 nm, 309 nm, 327 nm, 354 nm and 386 nm, and the emission wavelength peak was observed at 484 nm (excitation wavelength: 381 nm). [Example 5]

[0193] In this example, a light-emitting element 1 and a light-emitting element 2, each containing a dibenzo[f,h]quinoxaline derivative, and a comparative light-emitting element 3 were prepared. The structure of each light-emitting element is shown in Fig. 22. Chemical formulas of materials used in this example are shown below. < <Herstellung des Licht emittierenden Elements 1, des Licht emittierenden Elements 2 und des Licht emittierenden Vergleichselements 3> >

[0194] First, indium tin oxide containing silicon oxide (ITSO) was deposited over a glass substrate 1100 by a sputtering method, forming a first electrode 1101 serving as an anode. Note that the thickness of the first electrode 1101 was set to 110 nm, and the area of ​​the first electrode 1101 was set to 2 mm × 2 mm.

[0195] Subsequently, as a pretreatment for forming the light-emitting element 1, the light-emitting element 2, and the comparative light-emitting element 3 over the substrate 1100, a surface of the substrate was washed with water, baking was performed at 200 °C for 1 hour, and then UV ozone treatment was performed for 370 seconds.

[0196] The substrate 1100 was then transferred to a vacuum evaporation device in which the pressure was increased to about 10 -4Pa, and baked in a heating chamber of the vacuum evaporation device at 170 °C for 30 minutes in vacuum, and then the substrate 1100 was cooled for about 30 minutes.

[0197] Next, the substrate 1100 was mounted on a holder in the vacuum evaporation device such that a surface of the substrate 1100 over which the first electrode 1101 was formed faced downward. This example describes a case where a hole-injection layer 1111, a hole-transport layer 1112, a light-emitting layer 1113, an electron-transport layer 1114, and an electron-injection layer 1115, which are included in an EL layer 1102, were sequentially formed by a vacuum evaporation method.

[0198] After the pressure in the vacuum evaporation device has been reduced to 10 -4After the pressure was reduced to 100 Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) and molybdenum oxide were co-evaporated so that the mass ratio of DBT3P-II to molybdenum oxide was 4:2, thereby forming the hole-injection layer 1111 on the first electrode 1101. The thickness of the hole-injection layer 1111 was set to 20 nm. Note that co-evaporation is an evaporation method in which a plurality of different substances are simultaneously evaporated from the corresponding evaporation sources.

[0199] Then, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) was deposited to a thickness of 20 nm by evaporation, thereby forming the hole transport layer 1112.

[0200] Next, the light-emitting layer 1113 was formed on the hole transport layer 1112. In the case of the light-emitting element 1, 2-{3-[2-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq-02, which is represented by the structural formula (103)), N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) and (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]) were deposited in a thickness of 20 nm by co-evaporation, so that the mass ratio of 2mPCCzPDBq-02 to PCBBiF and [Ir(tBuppm)2(acac)] was 0.7:0.3:0.05. Then, 2mPCCzPDBq-02, PCBBiF, and [Ir(tBuppm)2(acac)] were co-deposited to a thickness of 20 nm by co-evaporation, so that the mass ratio of 2mPCCzPDBq-02 to PCBBiF and [Ir(tBuppm)2(acac)] was 0.8:0.2:0.05.In this way, the light-emitting layer 1113 was formed with a multilayer structure and a thickness of 40 nm.

[0201] In the case of the light-emitting element 2, 2-{3-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzPDBq, which is represented by the structural formula (101)), PCBBiF and [Ir(tBuppm)2(acac)] were deposited to a thickness of 20 nm by co-evaporation, so that the mass ratio of 2mPCCzPDBq to PCBBiF and [Ir(tBuppm)2(acac)] was 0.7:0.3:0.05. Then, 2mPCCzPDBq, PCBBiF, and [Ir(tBuppm)2(acac)] were co-evaporated to a thickness of 20 nm, such that the mass ratio of 2mPCCzPDBq to PCBBiF and [Ir(tBuppm)2(acac)] was 0.8:0.2:0.05. Thus, the light-emitting layer 1113 with a multilayer structure and a thickness of 40 nm was formed.

[0202] In the case of the light-emitting reference element 3, 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), PCBBiF and [Ir(tBuppm)2(acac)] were deposited in a thickness of 20 nm by co-evaporation, so that the mass ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(tBuppm)2(acac)] was 0.7:0.3:0.05. Then, 2mDBTBPDBq-II, PCBBiF, and [Ir(tBuppm)2(acac)] were co-evaporated to a thickness of 20 nm, such that the mass ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(tBuppm)2(acac)] was 0.8:0.2:0.05. Thus, the light-emitting layer 1113 with a multilayer structure and a thickness of 40 nm was formed.

[0203] Then, in the case of the light-emitting element 1, 2mPCCzPDBq-02 was deposited to a thickness of 20 nm on the light-emitting layer 1113 by evaporation, and then bathophenanthroline (abbreviation: Bphen) was deposited to a thickness of 10 nm by evaporation, thereby forming the electron-transport layer 1114. In the case of the light-emitting element 2, 2mPCCzPDBq was deposited to a thickness of 20 nm on the light-emitting layer 1113 by evaporation, and then bathophenanthroline (abbreviation: Bphen) was deposited to a thickness of 10 nm by evaporation, thereby forming the electron-transport layer 1114.In the case of the comparative light-emitting element 3, 2mDBTBPDBq-II was deposited to a thickness of 20 nm on the light-emitting layer 1113 by evaporation, and then bathophenanthroline (abbreviation: Bphen) was deposited to a thickness of 10 nm by evaporation, thereby forming the electron-transport layer 1114.

[0204] In addition, lithium fluoride was deposited to a thickness of 1 nm on the electron transport layer 1114 by evaporation, thereby forming the electron injection layer 1115.

[0205] Finally, aluminum was evaporated to a thickness of 200 nm on the electron injection layer 1115 to form a second electrode 1103 serving as a cathode; thus, light-emitting element 1, light-emitting element 2, and comparative light-emitting element 3 were fabricated. Note that in all of the above evaporation steps, evaporation was performed by a resistance heating method.

[0206] Table 1 shows the element structures of the light-emitting element 1, the light-emitting element 2 and the comparative light-emitting element 3, which were manufactured in the manner described above. [Table 1] ersteElektrode Lochinjektionsschicht Lochtransportschicht LichtemittierendeSchicht Elektronentransportschicht Elektroneninjektionsschicht zweiteElektrode LichtemittierendesElement 1 ITSO(110 nm) DBT3P-II:MoOx(4:2 20 nm) BPAFLP(20 nm) * 2mPCCzPDBq-02(20 nm) Bphen(10 nm) LiF(1 nm) Al (200 nm) LichtemittierendesElement 2 ITSO(110 nm) DBT3P-II:MoOx(4:2 20 nm) BPAFLP(20 nm) ** 2mPCCzPDBq(20 nm) Bphen(10 nm) LiF(1 nm) Al (200 nm) Light-emitting reference element 3 ITSO(110 nm) DBT3P-II:MoOx(4:2 20 nm) BPAFLP(20 nm) *** 2mDBTBPDBq-II(20 nm) Bphen(10 nm) LiF(1 nm) Al (200 nm) * 2mPCCzPDBq-02 : PCBBiF : [Ir(tBuppm)2(acac)] (0.7:0.3:0.05 (20 nm) \ 0.8:0.2:0.05 (20 nm)) ** 2mPCCzPDBq : PCBBiF : [Ir(tBuppm)2(acac)] (0.7:0.3:0.05 (20 nm) \ 0.8:0.2:0.05 (20 nm)) *** 2mDBTBPDBq-II : PCBBiF : [Ir(tBuppm)2(acac)] (0.7:0.3:0.05 (20 nm) \ 0.8:0.2:0.05 (20 nm))

[0207] The fabricated light-emitting element 1, light-emitting element 2, and comparative light-emitting element 3 were sealed in a glove box under a nitrogen atmosphere so that they were not exposed to the air (specifically, a sealant was applied to enclose the elements, UV treatment was performed, and heat treatment was performed at 80 °C for 1 hour). < <Betriebseigenschaften des Licht emittierenden Elements 1, des Licht emittierenden Elements 2 und des Licht emittierenden Vergleichselements 3> >

[0208] The operating characteristics of the fabricated light-emitting element 1, light-emitting element 2, and comparative light-emitting element 3 were measured. Note that the measurements were conducted at room temperature (in an atmosphere maintained at 25 °C). The results are shown in Fig. 23, Fig. 24, Fig. 25 and Fig.26 shown.

[0209] Table 2 shows the initial values ​​of the main characteristics of the light-emitting element 1, the light-emitting element 2 and the comparison light-emitting element 3 at a luminance of about 1000 cd / m 2 . [Table 2] Voltage (V) Current (mA) Current density (mA / cm 2 ) Chromaticity(x;y) Luminance (cd / m 2 ) Power efficiency (cd / A) Power efficiency (lm / W) external quantum efficiency (%) Light-emitting element 1 2,9 0,038 1,0 (0,42;0,57) 1100 110 120 29 Light-emitting element 2 2,8 0,033 0,8 (0,41;0,58) 920 110 120 29 Light-emitting reference element 3 2,9 0,035 0,88 (0,42;0,57) 980 110 120 30

[0210] Fig. Figure 27 shows the emission spectra of the light-emitting element 1, the light-emitting element 2 and the comparative light-emitting element 3, through which a current with a current density of 2.5 mA / cm 2 flows. As in Fig. As shown in Figure 27, the emission spectra of the light-emitting element 1, the light-emitting element 2, and the comparative light-emitting element 3 each have a peak at about 546 nm, which is attributed to [Ir(tBuppm)2(acac)].

[0211] Fig.28A shows the results of reliability tests on the light-emitting element 1, the light-emitting element 2 and the comparison light-emitting element 3. In Fig. 28A, the vertical axis represents the normalized luminance (%) assuming that the initial luminance is 100%, and the horizontal axis represents the operating time (h) of the elements. It should be noted that in the reliability tests, the light-emitting element 1, the light-emitting element 2, and the comparison light-emitting element 3 were operated under the conditions where the initial luminance was set to 5000 cd / m 2 was set and the current density was constant.

[0212] The results show that the light-emitting element 1 manufactured using 2mPCCzPDBq-02 and the light-emitting element 2 manufactured using 2mPCCzPDBq, which are embodiments of the present invention, have higher reliability and longer lifetime than the comparative light-emitting element 3 manufactured using 2mDBTBPDBq-II.

[0213] Fig.Figure 28B shows the measurement results of the voltage change magnitude in the reliability tests. The vertical axis represents the voltage change magnitude (V), and the horizontal axis represents the operating time (h) of the elements. These results show that the voltage increase magnitudes of light-emitting element 1 and light-emitting element 2, which were operated at a constant current, are smaller than those of comparison light-emitting element 3. For example, after the light-emitting elements were operated for about 500 hours, the voltage increase magnitude of comparison light-emitting element 3 was approximately 0.08 V, while those of light-emitting elements 1 and 2 were approximately 0.05 V and 0.02 V, respectively. In other words, the voltage increase magnitudes of light-emitting element 1 and light-emitting element 2 are approximately as small as 1 / 2 and 1 / 2, respectively.1 / 4 of that of the comparative light-emitting element 3, indicating a significant effect of an embodiment of the present invention.

[0214] It should be noted that the combination of PCBBiF and 2mPCCzPDBq-02, 2mPCCzPDBq, or 2mDBTBPDBq-II forms an exciplex (because the mixed film containing PCBBiF and any of these dibenzoquinoxaline compounds exhibits yellow-green light emission with a longer wavelength than the film containing only PCBBiF or the film containing only any of these dibenzoquinoxaline compounds). Furthermore, the HOMO levels of 2mPCCzPDBq-02, 2mPCCzPDBq, 2mDBTBPDBq-II, and PCBBiF are -5.69 eV, -5.63 eV, -6.22 eV, and -5.36 eV, respectively. The HOMO levels were obtained by cyclic voltammetry (CV) measurement.

[0215] Using the HOMO levels obtained as above, ΔE HOMOin the light-emitting layer of each light-emitting element. Table 3 shows the results. [Table 3] Δ E HOMO (house) Light-emitting element 1 0,33 Light-emitting element 2 0,27 Light-emitting reference element 3 0,86

[0216] According to the results, it is important that ΔE HOMO less than or equal to 0.4 eV, preferably less than or equal to 0.3 eV.

[0217] Furthermore, the HOMO level of BPAFLP, which is used for the hole-transport layer, is -5.51 eV. Consequently, the HOMO level of the third organic compound used for the hole-transport layer was found to be lower than the HOMO level of PCBBiF, the second organic compound, and to be between the HOMO level of PCBBiF, the second organic compound, and the HOMO level of the first organic compound (2mPCCzPDBq-02 or 2mPCCzPDBq). This is important because holes are injected not only into the second organic compound but also partially into the first organic compound. [Example 6]

[0218] In this example, a light-emitting element 4 containing a dibenzo[f,h]quinoxaline derivative was prepared. The structure of the light-emitting element is shown in Fig.22 as described in Example 5. Chemical formulas of materials used in this example are shown below. <<Herstellung des Licht emittierenden Elements 4> >

[0219] First, indium tin oxide containing silicon oxide (ITSO) was deposited over a glass substrate 1100 by a sputtering method, forming a first electrode 1101 serving as an anode. Note that the thickness of the first electrode 1101 was set to 110 nm, and the area of ​​the first electrode 1101 was set to 2 mm × 2 mm.

[0220] Subsequently, as a pretreatment for forming the light-emitting element 4 over the substrate 1100, a surface of the substrate was washed with water, baking was performed at 200 °C for 1 hour, and then UV ozone treatment was performed for 370 seconds.

[0221] The substrate 1100 was then transferred to a vacuum evaporation device in which the pressure was increased to about 10 -4 Pa, and baked in a heating chamber of the vacuum evaporation device at 170 °C for 30 minutes in vacuum, and then the substrate 1100 was cooled for about 30 minutes.

[0222] Next, the substrate 1100 was mounted on a holder in the vacuum evaporation apparatus such that a surface of the substrate 1100 over which the first electrode 1101 was formed faced downward. This example describes a case where a hole-injection layer 1111, a hole-transport layer 1112, a light-emitting layer 1113, an electron-transport layer 1114, and an electron-injection layer 1115, which are included in an EL layer 1102, were sequentially formed by a vacuum evaporation method.

[0223] After the pressure in the vacuum evaporation device has been reduced to 10 -4 After the pressure was reduced to 100 Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) and molybdenum oxide were co-evaporated so that the mass ratio of DBT3P-II to molybdenum oxide was 4:2, thereby forming the hole-injection layer 1111 on the first electrode 1101. The thickness of the hole-injection layer 1111 was set to 20 nm. Note that co-evaporation is an evaporation method in which a plurality of different substances are simultaneously evaporated from the corresponding evaporation sources.

[0224] Then, 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP) was deposited to a thickness of 20 nm by evaporation, thereby forming the hole transport layer 1112.

[0225] Next, the light-emitting layer 1113 was formed on the hole transport layer 1112. By co-evaporation, 2-{4-[2-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}dibenzo[f,h]quinoxaline (abbreviation: 2PCCzPDBq-02, which is represented by the structural formula (102)), N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]) were deposited in a thickness of 20 nm, so that the mass ratio of 2PCCzPDBq-02 to PCBBiF and [Ir(dppm)2(acac)] was 0.7:0.3:0.05. Then, 2PCCzPDBq-02, PCBBiF, and [Ir(dppm)2(acac)] were co-deposited to a thickness of 20 nm by co-evaporation, such that the mass ratio of 2PCCzPDBq-02 to PCBBiF and [Ir(dppm)2(acac)] was 0.8:0.2:0.05. Thus, the light-emitting layer 1113 with a multilayer structure and a thickness of 40 nm was formed.

[0226] Then, 2PCCzPDBq-02 was deposited to a thickness of 20 nm on the light-emitting layer 1113 by evaporation, and then bathophenanthroline (abbreviation: Bphen) was deposited to a thickness of 10 nm by evaporation, thereby forming the electron-transport layer 1114.

[0227] In addition, lithium fluoride was deposited to a thickness of 1 nm on the electron transport layer 1114 by evaporation, thereby forming the electron injection layer 1115.

[0228] Finally, aluminum was evaporated to a thickness of 200 nm on the electron-injection layer 1115 to form the second electrode 1103 serving as the cathode; thus, the light-emitting element 4 was fabricated. Note that in all of the above evaporation steps, evaporation was performed by a resistance heating method.

[0229] Table 4 shows the element structure of the light-emitting element 4, which was manufactured in the manner described above. [Table 4] first electrode Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer second electrode Light-emitting element 4 ITSO(110 nm) DBT3P-II:MoOx(4:2 20 nm) BPAFLP(20 nm) * 2PCCzPDBq-02(20 nm) Bphen(10 nm) LiF (1 nm) Al(200 nm) * 2PCCzPDBq-02 : PCBBiF : [Ir(dppm)2(acac)] (0.7:0.3:0.05 (20 nm) \ 0.8:0.2:0.05 (20 nm))

[0230] The fabricated light-emitting element 4 was sealed in a glove box under a nitrogen atmosphere so that it was not exposed to the air (specifically, a sealant was applied to enclose the element, a UV treatment was performed, and a heat treatment was performed at 80 °C for 1 hour). <<Betriebseigenschaften des Licht emittierenden Elements 4> >

[0231] The operating characteristics of the fabricated light-emitting element 4 were measured. Note that the measurements were conducted at room temperature (in an atmosphere maintained at 25 °C). The results are shown in Fig. 29, Fig. 30, Fig. 31 and Fig. 32 shown.

[0232] Table 5 shows the initial values ​​of the main characteristics of the light-emitting element 4 at a luminance of about 1000 cd / m 2 . [Table 5] Voltage (V) Current (mA) Current density (mA / cm 2 ) Chromaticity(x;y) Luminance (cd / m 2 ) Power efficiency (cd / A) Power efficiency (Im / W) external quantum efficiency (%) Light-emitting element 4 2,8 0,045 1,1 (0,56;0,44) 910 81 91 30

[0233] Fig. 33 shows the emission spectrum of the light-emitting element 4, through which a current with a current density of 2.5 mA / cm 2 flows. As in Fig. 33, the emission spectrum of the light-emitting element 4 has a peak at about 581 nm, which is attributed to [Ir(dppm)2(acac)].

[0234] Fig. 34A shows the results of a reliability test on the light-emitting element 4. In Fig.34A, the vertical axis represents the normalized luminance (%) assuming that the initial luminance is 100%, and the horizontal axis represents the operating time (h) of the element. It should be noted that in the reliability test, the light-emitting element 4 was operated under the conditions where the initial luminance was set to 5000 cd / m 2 was set and the current density was constant.

[0235] The results show that the light-emitting element 4 manufactured using 2PCCzPDBq-02, which is an embodiment of the present invention, has high reliability and a long lifetime.

[0236] Fig.Figure 34B shows the measurement results of the voltage change magnitude in the reliability test. The vertical axis represents the voltage change magnitude (V), and the horizontal axis represents the operating time (h) of the element. The results show that the voltage increase magnitude of the light-emitting element 4 operated at a constant current is small. For example, after the light-emitting element 4 was operated for about 500 hours, the voltage increase magnitude was approximately 0.01 V. A comparative light-emitting element 9 was manufactured using 2mDBTBPDBq-II instead of 2PCCzPDBq-02 in the light-emitting element 4 and operated under conditions similar to those of the light-emitting element 4. In this case, the voltage increase magnitude was approximately 0.06 V after the comparative light-emitting element 9 was operated for about 500 hours.In other words, the amount of voltage rise of the light-emitting element 4 is approximately as small as 1 / 6 of that of the comparative light-emitting element 9, indicating a significant effect of an embodiment of the present invention.

[0237] It should be noted that the combination of 2PCCzPDBq-02 and PCBBiF forms an exciplex (because the mixed film containing this dibenzoquinoxaline compound and PCBBiF exhibits green light emission with a longer wavelength than the film containing only this dibenzoquinoxaline compound or the film containing only PCBBiF). In addition, ΔE HOMO in the light-emitting layer of the light-emitting element 4 is 0.32 eV, because the HOMO level of 2PCCzPDBq-02 is -5.68 eV. Consequently, it is important that ΔE HOMO is less than or equal to 0.4 eV.

[0238] Furthermore, the HOMO level of BPAFLP, which is used for the hole-transport layer, is -5.51 eV. Consequently, the HOMO level of the third organic compound used for the hole-transport layer was found to be lower than the HOMO level of PCBBiF, the second organic compound, and to be between the HOMO level of PCBBiF, the second organic compound, and the HOMO level of the first organic compound (2PCCzPDBq-02). This is important because holes are injected not only into the second organic compound but also partially into the first organic compound. [Example 7]<<Synthesebeispiel 5> >

[0239] This example describes a synthetic method for 2-{3'-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]biphenyl-3-yl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzBPDBq, represented by structural formula (122)). The structure of 2mPCCzBPDBq is shown below. <Synthese von 2-{3'-[3-(N-Phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]biphenyl-3-yl}dibenzo[f,h] chinoxalin (Abkürzung: 2mPCCzBPDBq)>

[0240] First, 2.0 g (4.3 mmol) of 2-(3'-bromobiphenyl-3-yl)dibenzo[f,h]quinoxaline, 1.8 g (4.3 mmol) of 3-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole, and 0.83 g (8.6 mmol) of sodium tert-butoxide were added to a 100 mL three-necked flask and mixed, and the air in the flask was replaced with nitrogen. 22 mL of mesitylene was added to this mixture, and the resulting mixture was degassed by stirring while reducing the pressure in the flask.

[0241] Subsequently, 25 mg (0.040 mmol) of bis(dibenzylideneacetone)palladium(0) (abbreviation: Pd(dba)2) and 35 mg (0.09 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (abbreviation: S-Phos) were added to this mixture. This mixture was stirred at 150 °C for 23 hours under a nitrogen stream. After a predetermined time, water and toluene were added to this mixture, and an aqueous layer of the obtained filtrate was subjected to extraction with toluene. The obtained extract solution and an organic layer were combined, washed with an aqueous solution of sodium bicarbonate and a saturated saline solution, and dried with magnesium sulfate. The obtained mixture was subjected to gravity filtration, and the filtrate was concentrated to obtain an oily substance. The oily substance was dissolved in toluene, and this solution was subjected to suction filtration through a layered arrangement of Celite and alumina.The obtained filtrate was concentrated to obtain a brown oily substance. This oily substance was purified by high-performance liquid chromatography. Column chromatography was performed using chloroform as the eluent (pressure: 4.5 MPa, flow rate: 100 mL / min, holding time: 45 minutes, and injection volume: 0.9 g / 30 mL). The obtained fraction was concentrated and recrystallized with hexane to obtain 0.66 g of a yellow powder, which was the target substance, in an 18% yield.

[0242] Using a train sublimation process, 0.66 g of the resulting yellow powdery solid, which was the target substance, was purified. The sublimation purification was carried out at 385 °C under a pressure of 2.6 Pa with an argon gas flow rate of 5 ml / min. After the sublimation purification, 0.5 g of a yellow, glassy solid of 2mPCCzBPDBq was obtained with a collection rate of 83%. The synthesis scheme for this step is shown in Scheme (e-1) below.

[0243] Analysis results obtained by nuclear magnetic resonance spectroscopy ( 1 H-NMR) of the yellow powdery solid obtained in the above step are described below. 1 H-NMR diagrams are in Fig. 35A and Fig. 35B shown. Fig. Figure 35B is a diagram in which the range from 7.0 (ppm) to 10 (ppm) is plotted on the horizontal axis (δ) in Fig.35A. These results indicate that 2-{3'-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]biphenyl-3-yl}dibenzo[f,h]quinoxaline (abbreviation: 2mPCCzBPDBq, which is represented by the structural formula (122)) was obtained in the above step.

[0244] 1 H-NMR (CDCl3, 500 MHz): δ (ppm) = 7.30-7.37 (m, 2H), 7.41-7.53 (m, 5H), 7.59-7.89 (m, 18H), 8.04 (dd, J = 1.7 Hz, 1H), 8.23 ​​(d, J = 7.5 Hz, 1H), 8.28 (d, 8.0 Hz, 1H), 8.35 (d, J = 8.0 Hz, 1H), 8.48 (dd, J = 11.4 Hz, J = 1.7 Hz, 2H), 8.66 (d, J = 8.1 Hz, 1H), 8.70 (s, 1H), 9.25 (dd, J = 6.3 Hz, J = 1.1 Hz, 1H), 9.43 (dd, J = 7.5 Hz, J = 1.7 Hz, 1H), 9.47 (s, 1H). [Example 8]

[0245] In this example, a light-emitting element 5 containing the dibenzo[f,h]quinoxaline derivative, 2mPCCzPDBq, represented by structural formula (101) and an embodiment of the present invention, a comparative light-emitting element 6 containing a comparative material, 2mDBTPDBq-II, and a comparative light-emitting element 7 containing a comparative material, 2-[3-(9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzPDBq), were prepared. A manufacturing method of each light-emitting element is substantially the same as that in Example 5 and is therefore omitted. Chemical formulas of materials used in this example are shown below. < <Herstellung des Licht emittierenden Elements 5, des Licht emittierenden Vergleichselements 6 und des Licht emittierenden Vergleichselements 7> >

[0246] Table 6 shows the element structures of the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7 manufactured in this example. [Table 6] first electrode Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer second electrode Light-emitting element 5 ITO (110 nm) DBT3P-II:MoOx(4:2 20 nm) BPAFLP(20 nm) * 2mPCCzPDBq(20 nm) Bphen(10 nm) LiF (1 nm) Al(200 nm) Light-emitting reference element 6 ITO (110 nm) DBT3P-II:MoOx(4:2 20 nm) BPAFLP(20 nm) ** 2mDBTPDBq-II(20 nm) Bphen(10 nm) LiF (1 nm) Al(200 nm) Light-emitting reference element 7 ITO (110 nm) DBT3P-II:MoOx(4:2 20 nm) BPAFLP(20 nm) *** 2mCzPDBq(20 nm) Bphen(10 nm) LiF (1 nm) Al(200 nm) * 2mPCCzPDBq : PCBBiF : [Ir(tBuppm)2(acac)] (0.7:0.3:0.05 (20 nm) \ 0.8:0.2:0.05 (20 nm)) ** 2mDBTPDBq-II : PCBBiF : [Ir(tBuppm)2(acac)] (0.7:0.3:0.05 (20 nm) \ 0.8:0.2:0.05 (20 nm)) *** 2mCzPDBq : PCBBiF : [Ir(tBuppm)2(acac)] (0.7:0.3:0.05 (20 nm) \ 0.8:0.2:0.05 (20 nm))

[0247] The fabricated light-emitting element 5, comparative light-emitting element 6, and comparative light-emitting element 7 were sealed in a glove box under a nitrogen atmosphere so that they were not exposed to the air (specifically, a sealant was applied to enclose the elements, UV treatment was performed, and heat treatment was performed at 80 °C for 1 hour). < <Betriebseigenschaften des Licht emittierenden Elements 5, des Licht emittierenden Vergleichselements 6 und des Licht emittierenden Vergleichselements 7> >

[0248] The operating characteristics of the fabricated light-emitting element 5, comparative light-emitting element 6, and comparative light-emitting element 7 were measured. Note that the measurements were conducted at room temperature (in an atmosphere maintained at 25°C).

[0249] Fig. 36 shows the current density-luminance characteristics, Fig. 37 shows the voltage-luminance characteristics, Fig. 38 shows the luminance-current efficiency characteristics, and Fig. Figure 39 shows the voltage-current characteristics of each light-emitting element.

[0250] Table 7 shows the initial values ​​of the main characteristics of the light-emitting element 5, the comparative light-emitting element 6 and the comparative light-emitting element 7 at a luminance of about 1000 cd / m 2 . [Table 7] Voltage (V) Current (mA) Current density (mA / cm 2 ) Chromaticity(x;y) Luminance (cd / m 2 ) Power efficiency (cd / A) Power efficiency (Im / W) external quantum efficiency (%) Light-emitting element 5 2,8 0,047 1,2 (0,42;0,57) 1100 95 110 25 Light-emitting reference element 6 3,0 0,044 1,1 (0,43;0,56) 990 90 94 24 Light-emitting reference element 7 2,9 0,060 1,5 (0,41;0,58) 940 63 68 16

[0251] Fig.Figure 40 shows the emission spectra of the light-emitting element 5, the comparative light-emitting element 6 and the comparative light-emitting element 7, through which a current with a current density of 2.5 mA / cm 2 flows. As in Fig. 40, the emission spectra of the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7 each have a peak at about 544 nm, which is attributed to [Ir(tBuppm)2(acac)].

[0252] Fig. 41A shows the results of reliability tests on the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7. In Fig.41A, the vertical axis represents the normalized luminance (%) assuming that the initial luminance is 100%, and the horizontal axis represents the operating time (h) of the elements. It should be noted that in the reliability tests, the light-emitting element 5, the comparative light-emitting element 6, and the comparative light-emitting element 7 were operated under the conditions where the initial luminance was set to 5000 cd / m 2 was set and the current density was constant.

[0253] The results show that the light-emitting element 5 fabricated using 2mPCCzPDBq, which is an embodiment of the present invention, has higher reliability and longer lifetime than the comparative light-emitting element 6 fabricated using 2mDBTPDBq-II and the comparative light-emitting element 7 fabricated using 2mCzPDBq.

[0254] Fig.Figure 41B shows the measurement results of the voltage change magnitude in the reliability tests. The vertical axis represents the voltage change magnitude (V), and the horizontal axis represents the operating time (h) of the elements. These results show that the voltage rise magnitude of the light-emitting element 5 operated at a constant current is smaller than those of the comparative light-emitting elements 6 and 7. For example, after the light-emitting elements were operated for about 1000 hours, the voltage rise magnitude of the comparative light-emitting element 6 was approximately 0.31 V, that of the comparative light-emitting element 7 was approximately 0.50 V, while that of the light-emitting element 5 was approximately 0.04 V.In other words, the amount of voltage rise of the light-emitting element 5 is much smaller than those of the comparative light-emitting elements 6 and 7, indicating a significant effect of an embodiment of the present invention.

[0255] Note that the combination of PCBBiF and 2mPCCzPDBq, 2mDBTPDBq-II, or 2mCzPDBq forms an exciplex (because the mixed film containing PCBBiF and any of these dibenzoquinoxaline compounds exhibits yellow-green light emission with a longer wavelength than the film containing only PCBBiF or the film containing only any of these dibenzoquinoxaline compounds). Furthermore, the HOMO levels of 2mPCCzPDBq, 2mDBTPDBq-II, 2mCzPDBq, and PCBBiF are -5.63 eV, -6.22 eV, -5.91 eV, and -5.36 eV, respectively. The HOMO levels were obtained by cyclic voltammetry (CV) measurement.

[0256] Using the HOMO levels obtained as above, ΔE HOMO in the light-emitting layer of each light-emitting element. Table 8 shows the results. [Table 8] ΔE HOMO (eV) Light-emitting element 5 0,27 Light-emitting reference element 6 0,86 Light-emitting reference element 7 0,55

[0257] According to the results, it is important that ΔE HOMO less than or equal to 0.4 eV, preferably less than or equal to 0.3 eV.

[0258] Furthermore, the HOMO level of BPAFLP, which is used for the hole-transport layer, is -5.51 eV. Consequently, the HOMO level of the third organic compound used for the hole-transport layer was found to be lower than the HOMO level of PCBBiF, the second organic compound, and to be between the HOMO level of PCBBiF, the second organic compound, and the HOMO level of the first organic compound (2mPCCzPDBq). This is important because holes are injected not only into the second organic compound but also partially into the first organic compound. [Example 9]

[0259] In this example, a light-emitting element 8 containing the dibenzo[f,h]quinoxaline derivative, 2mPCCzBPDBq, was prepared, which is an embodiment of the present invention. A manufacturing method of the light-emitting element 8 is essentially the same as that in Example 5 and is therefore omitted. Chemical formulas of materials used in this example are shown below. <<Herstellung des Licht emittierenden Elements 8> >

[0260] Table 9 shows the element structure of the light-emitting element 8 manufactured in this example. [Table 9] first electrode Hole injection layer Hole transport layer Light-emitting layer Electron transport layer Electron injection layer second electrode Light-emitting element 8 ITO (110 nm) DBT3P-II:MoOx(4:2 60 nm) BPAFLP(20 nm) * 2mPCCzBPDBq(20 nm) Bphen(10 nm) LiF (1 nm) Al(200 nm) * 2mPCCzBPDBq : PCBBiF : [Ir(dppm)2(acac)] (0.7:0.3:0.05 (20 nm) / 0.8:0.2:0.05 (20 nm))

[0261] The fabricated light-emitting element 8 was sealed in a glove box under a nitrogen atmosphere so that it was not exposed to the air (specifically, a sealant was applied to enclose the element, a UV treatment was performed, and a heat treatment was performed at 80 °C for 1 hour). <<Betriebseigenschaften des Licht emittierenden Elements 8> >

[0262] The operating characteristics of the fabricated light-emitting element 8 were measured. Note that the measurements were conducted at room temperature (in an atmosphere maintained at 25°C).

[0263] Fig. 42 shows the current density-luminance characteristics, Fig. 43 shows the voltage-luminance characteristics, Fig. 44 shows the luminance-power efficiency characteristics, and Fig. Figure 45 shows the voltage-current characteristics of the light-emitting element 8.

[0264] Table 10 shows the initial values ​​of the main characteristics of the light-emitting element 8 at a luminance of about 1000 cd / m 2 . [Table 10] Voltage (V) Current (mA) Current density (mA / cm 2 ) Chromaticity(x;y) Luminance (cd / m 2 ) Power efficiency (cd / A) Power efficiency (Im / W) externeQuanteneffizienz (%) LichtemittierendesElement 8 3,0 0,046 1,2 (0,56;0,44) 900 78 82 30

[0265] Fig. 46 shows the emission spectrum of the light-emitting element 8, through which a current with a current density of 2.5 mA / cm 2 flows. As in Fig. 46, the emission spectrum of the light-emitting element 8 has a peak at about 584 nm, which is attributed to [Ir(dppm)2(acac)]. [Example 10]

[0266] In this example, a light-emitting element which is an embodiment of the present invention was manufactured and subjected to a preservation test.

[0267] In this example, a light-emitting element 1A, a light-emitting element 2A, a comparative light-emitting element 3A, a light-emitting element 4A, and a light-emitting element 8A were manufactured. The structure and manufacturing method of the light-emitting element 1A are the same as those of the light-emitting element 1 in Example 5. The structure and manufacturing method of the light-emitting element 2A, those of the comparative light-emitting element 3A, those of the light-emitting element 4A, and those of the light-emitting element 8A are the same as those of the light-emitting element 2 in Example 5, those of the comparative light-emitting element 3 in Example 5, those of the light-emitting element 4 in Example 6, and those of the light-emitting element 8 in Example 9, respectively.

[0268] In the preservation tests of this example, the light-emitting elements were each preserved in a thermostatic oven maintained at 100°C for a predetermined period of time, and the operating characteristics were measured. Note that the operating characteristics were measured at room temperature (in an atmosphere maintained at 25°C) after the light-emitting elements were removed from the thermostatic oven.

[0269] Fig. 47 shows the voltage-current characteristics and Fig. Figure 48 shows the luminance-external quantum efficiency characteristics of the light-emitting element 1A after preservation at 100 °C for a predetermined period of time. Fig. 47, the horizontal axis represents the voltage (V), and the vertical axis represents the current (mA). In Fig. 48 the horizontal axis represents the luminance (cd / m 2), and the vertical axis represents the external quantum efficiency (%).

[0270] Fig. 49 shows the voltage-current characteristics and Fig. Figure 50 shows the luminance-external quantum efficiency characteristics of the light-emitting element 2A after preservation at 100 °C for a predetermined period of time. Fig. 49, the horizontal axis represents the voltage (V), and the vertical axis represents the current (mA). In Fig. 50 the horizontal axis represents the luminance (cd / m 2 ), and the vertical axis represents the external quantum efficiency (%).

[0271] Fig. 51 shows the voltage-current characteristics and Fig. Figure 52 shows the luminance-external quantum efficiency characteristics of the comparative light-emitting element 3A after preservation at 100 °C for a predetermined period of time. Fig. 51 the horizontal axis represents the voltage (V) and the vertical axis represents the current (mA). In Fig. 52 the horizontal axis represents the luminance (cd / m 2 ), and the vertical axis represents the external quantum efficiency (%). Since no light emission was observed in the light-emitting element preserved for 20 hours, Fig. 52 no data on the luminance-external quantum efficiency properties after preservation for 20 hours.

[0272] Fig. 53 shows the voltage-current characteristics and Fig. Figure 54 shows the luminance-external quantum efficiency characteristics of the light-emitting element 4A after preservation at 100 °C for a predetermined period of time. Fig. 53 the horizontal axis represents the voltage (V) and the vertical axis represents the current (mA). In Fig. 54 the horizontal axis represents the luminance (cd / m 2), and the vertical axis represents the external quantum efficiency (%).

[0273] Fig. 55 shows the voltage-current characteristics and Fig. Figure 56 shows the luminance-external quantum efficiency characteristics of the light-emitting element 8A after preservation at 100 °C for a predetermined period of time. Fig. 55 the horizontal axis represents the voltage (V) and the vertical axis represents the current (mA). In Fig. 56 the horizontal axis represents the luminance (cd / m 2 ), and the vertical axis represents the external quantum efficiency (%).

[0274] Fig. 47 to Fig. 50 and Fig. 53 to Fig. 56 show that for light-emitting element 1A, light-emitting element 2A, light-emitting element 4A, and light-emitting element 8A, the voltage-current characteristics and the luminance-external quantum efficiency characteristics changed only slightly even after being preserved at 100 °C for 500 hours, and that the element properties hardly deteriorated due to high-temperature preservation. In contrast, Fig. 51 and Fig. 52 that the voltage-current characteristics and the luminance-external quantum efficiency characteristics of the comparative light-emitting element 3A changed significantly after being preserved at 100 °C, and that the element properties deteriorated due to high-temperature preservation. As shown in Fig. 51, in the comparative light-emitting element 3A, an initial insulating property is not maintained after 100 hours, and a leakage current is generated. Fig. 52 indicates a defect, i.e., no light emission from the element. The above results demonstrate that the heat resistance of a light-emitting element according to the invention is significantly improved when preserved at high temperatures.

Claims

[1] Light-emitting element comprising: a light-emitting layer between an anode and a cathode, wherein the light-emitting layer contains a first organic compound, a second organic compound and a light-emitting substance which converts triplet excitation energy into light emission, wherein the first organic compound and the second organic compound are mixed in the light-emitting layer, wherein a combination of the first organic compound and the second organic compound forms an exciplex, wherein the first organic compound comprises a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, wherein the six-membered nitrogen-containing heteroaromatic ring is pyrazine, pyridazine, triazine or tetrazine, wherein the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound, and wherein a difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.4 eV. [2] Light-emitting element comprising: a light-emitting layer between an anode and a cathode, wherein the light-emitting layer contains a first organic compound, a second organic compound and a light-emitting substance which converts triplet excitation energy into light emission, wherein the first organic compound and the second organic compound are mixed in the light-emitting layer, wherein a combination of the first organic compound and the second organic compound forms an exciplex, wherein the first organic compound comprises a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, wherein the six-membered nitrogen-containing heteroaromatic ring is pyrazine, pyridazine, triazine or tetrazine, wherein the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound, and wherein a difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.3 eV. [3] Light-emitting element comprising: a light-emitting layer between an anode and a cathode, wherein the light-emitting layer contains a first organic compound, a second organic compound and a light-emitting substance which converts triplet excitation energy into light emission, wherein a combination of the first organic compound and the second organic compound forms an exciplex, wherein the first organic compound comprises a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, where the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound, wherein a difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.4 eV, and wherein a benzene ring is condensed with the six-membered nitrogen-containing heteroaromatic ring. [4] Light-emitting element comprising: a light-emitting layer between an anode and a cathode, wherein the light-emitting layer contains a first organic compound, a second organic compound and a light-emitting substance which converts triplet excitation energy into light emission, wherein a combination of the first organic compound and the second organic compound forms an exciplex, wherein the first organic compound comprises a six-membered nitrogen-containing heteroaromatic ring and a carbazole skeleton, where the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound, wherein a difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.3 eV, and wherein a benzene ring is condensed with the six-membered nitrogen-containing heteroaromatic ring. [5] The light-emitting element according to claim 3 or 4, wherein the six-membered nitrogen-containing heteroaromatic ring is pyridine, pyrazine, pyrimidine, pyridazine, triazine or tetrazine. [6] The light-emitting element according to claim 3 or 4, wherein the six-membered nitrogen-containing heteroaromatic ring condensed with the benzene ring is quinoline, isoquinoline, dibenzo[f,h]quinolone, naphthyridine, dibenzo[f,h]quinoxaline or dibenzo[f,h]quinazoline. [7] A light-emitting device comprising the light-emitting element according to any one of claims 1 to 6. [8] Electronic device comprising: the light-emitting device according to claim 7; and a connection port or an operating button. [9] Lighting device comprising: the light-emitting device according to claim 7; and a housing. [10] The light-emitting element according to claim 3 or 4, wherein the first organic compound and the second organic compound are mixed in the light-emitting layer. [11] A light-emitting element according to any one of claims 1 to 4, wherein the HOMO levels are obtained by a cyclic voltammetry (CV) measurement.

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